Online learning, utilizing the Internet for access to materials and knowledge, involves students interacting with teachers and peers to enhance their learning experiences (Ally, 2004). Amid the epidemic, research has predominantly focused on students' perceptions of online learning amid contextual shifts. Studies have explored holistic aspects such as social presence, interaction, and satisfaction in comparison to face-to-face learning (Bali and Liu, 2018; Conrad et al., 2022). Additionally, research has delved into perceived differences in knowledge and skill acquisition between students and teachers (Syauqi et al., 2020), encountered barriers in psychology, technicity, and academia during online learning (Gonzalez-Ramirez et al., 2021), and varied experiences of students across different dimensions and countries (Cranfield et al., 2021).

Another set of research delved into more specific aspects. Some papers focused on factors affecting students' online learning performance, revealing that computer/Internet self-efficacy directly impacted course satisfaction (Wei and Chou, 2020). Martin and Bolliger (2018) explored students' perception of engagement strategies in online courses, finding that learner-to-instructor engagement strategies were highly valued. Previous research investigated undergraduates' experiences with and preferences for popular online learning applications during COVID-19 (Hendrawaty et al., 2021). Studies also examined how students' trust in their capacity to learn online, self-discipline plans, and confidence in using online learning platforms could predict their satisfaction and perceived usefulness of e-learning (Landrum, 2020). Addressing cultural diversity, Kumi-Yeboah et al. (2022) focused on minority students' online learning perceptions, highlighting the significance of diverse cultural experiences in online learning environments. Despite these diverse perspectives, existing research often dissects students' online learning perceptions into independent parts without establishing correlations and logical associations. Hence, there is a valuable opportunity for in-depth exploration in this area.

Online learning motivations significantly influence students' behaviors and outcomes, with studies highlighting their importance (Hartnett, 2016). Factors influencing and impacting engagement (Kim and Frick, 2011; Abdous, 2019; Esra and Sevilen, 2021) and achievement in online learning motivations have been explored (Lim and Kim, 2003; Dunn and Kennedy, 2019). Common causes include interest in the topic, sharing expertise, and relationship development, demonstrating complementary motivations among participants with different areas and levels of expertise (Gilbert, 2018). Understanding the mechanisms behind learning motivation is crucial, as these variables play a significant role in predicting students' learning success (Credé and Phillips, 2011). Research indicates lower motivation levels among online students compared to face-to-face students (Stark, 2019). Addressing this, some studies advocate for incorporating game dynamics to support natural learning motivation (Kam and Umar, 2018). Examining the association between students' game-playing motivations and gamification elements in higher education, researchers suggest tailoring gamification efforts to engage and motivate students of different levels (Jaskari and Syrjälä, 2022). The widely implemented self-determination theory has been applied to investigate the influence mechanisms and impacts of online learning's preparation level and learning engagement (Bovermann et al., 2018; Chiu, 2022). Students with a relatively low level of preparation exhibit non-autonomous motivation (Bovermann et al., 2018). However, further exploration is needed to understand how the self-determination theory operates in students' more profound online learning experiences.

When large-scale online learning is launched, more attention is paid to how interaction is carried out under the human-computer-human learning format and the impact of motivation and interaction on online learning participation and outcomes. For the interactions, some scholars explored the many types of connection and the multidimensional characteristics of communication in online learning settings (Vlachopoulos and Makri, 2019); how was interpersonal interaction measured (Mehall, 2020); the associations between online interactions and engagement (Purarjomandlangrudi and Chen, 2020). Interactions are a necessary part of online learning. Its primary purpose is to enhance students' learning effectiveness.

Therefore, students' perception of engagement strategies implemented in e-learning based on the interaction framework is critical (Martin and Bolliger, 2018). Domina et al. (2021) thought that learners with advanced technological skills interact more deeply. Some papers assessing online learning engagement suggested that perceived learning satisfaction predicts learning engagement in online learning courses (Chan et al., 2021). Besides, the online assessment conducted among students is tightly connected with online techniques and environment (Spitzer et al., 2021). Based on various forms of engagement, a study showed the outcomes of real-time online learning. It was shown that student academic outcomes are more significantly impacted by cognitive and behavioral involvement (Kobicheva, 2022).

From the former studies, online learning perception is an issue resulting from the swift learning methods. The subjects under discussion are no matter the perceptions' consequences, online learning's start (motivation), process (interaction and engagement), and outcomes. There are many significances in prior research. Nevertheless, the components of online learning are rarely viewed as a continuous, interacting, and logically related whole. This study intends to take a theoretical approach based on The Grounded Theory to the various aspects of students' online learning to connect them into a logical “storyline”. By doing so, insights into the underlying connotations and deeper reasons behind the perceptions of widespread online learning will be helpful to construct a corresponding theoretical framework.

This study's sample selection was mainly based on undergraduates from universities in Macau, supplemented by choosing students from universities in neighboring areas as auxiliary and external validity test samples. Macau is a small region with ten universities, four public and six privates. The main reasons for choosing students in Macau as the research participants are as follows. First, Macau is a multicultural region. College students have cultural characteristics from different countries and areas. The teaching language is mainly English. Learners from various cultures absorb their cultural practices in different ways, and there are cultural differences in their perceptions and how their basic needs are met (Ryan and Deci, 2020). Therefore, it is possible to conduct the study with mainly Macau university students, which is more representative and generalizable. Second, Macau universities admit a more significant proportion of mainland Chinese students. The admission criteria of these students are the first batch of admission marks in the Chinese college entrance examination, with higher academic standards, representing a higher quality group among universities. Third, more than half of local high school students in Macau go abroad for further studies. Those who stay in local universities have weaker academic standards and cultural backgrounds significantly different from those of mainland students (Su et al., 2022). Fourth, according to the government's plan, a certain percentage of international students are enrolled in Macau universities. This group of students also mainly receives subject education, which is typical of online classroom learning interaction and perception.

From July 2023 to October 2023, 56 undergraduates (18 male and 38 female) participated in the data collection process either face-to-face or online. Sampling methods included typical sampling, theoretical sampling, random sampling, and others. In July 2023, the sampling was mainly focused on one public university P in Macao, and the researchers sampled a total of 15 college students in the fields of Humanities and Languages, Public Administration and Social Sciences, and Medicine and Exercise Physiology, with typical and random sampling (see below for the basis and method of sampling); and in September, the sampling was continued in college P, another public university M, a private university C and neighboring areas based on the constant sampling principle. A total of 24 college students were added to the sampling, including those majoring in Tourism, Artificial Intelligence, and Education in Social Sciences. After the second round of sampling was completed, based on the results of coding and sorting, the researcher still felt the lack of many properties and dimensions under the deductive logic in the process of writing the article, and the research team decided to conduct focus interviews in three times in October 2023 through a combination of random sampling and theoretical sampling by sampling a total of 17 college students of the above-mentioned majors in University P again.

The research team developed a semi-structured interview outline in advance, which included demographic information; characteristics of online classes (such as time, space, content, activities, and materials); adaptability of online learning (process and assessment); online learning technologies (software, facilities, and their impacts); interactivity of online learning; engagement and effectiveness of online learning (including cognition, emotions, skills, behaviors and so on); and improvements in online learning. Specific interview questions were based on this framework. Follow-up questions will be posed to the interviewees, particularly when significant discourses or metaphors that contribute to research questions and theory development are identified. These insights will serve as the foundation for subsequent theoretical sampling. After obtaining ethical permission and verbal consent from the students interviewed, the in-depth interviews were recorded and transcribed into transcripts. The interviewees were coded in a four-level format, for example (M, F)–(SS, H, S)–(M, O)–230920. Represents (Male, Female)–(Social Science Major, Humanities Major, Science Major)–(Macau, Outside Macau)–Interview date 20th, September 2023.

The study drew primarily on The Grounded Theory introduced by Strauss and Corbin (1990) and Corbin and Strauss (2014). In keeping with the principle of theory formation based on empirical data, we used the constant comparative method to explore the “core category” of college students' perceptions of online learning (Hallberg, 2006). The data collection, analysis, and theoretical model generation were carried out alternately. In the process of the study, we maintained a constant comparison with the theory and literature based on the logical sequence formed by the data analysis to ensure the reliability and validity of the research findings.

In the initial sampling stage, a targeted approach involved selecting two local Macau students, one Mainland student, and one international student for in-depth interviews. Transcripts were then analyzed using the first-level coding procedures of Grounded Theory (Strauss and Corbin, 1990). Researchers conceptualized interview scripts, assigning conceptual names based on generalizations or intuitive phenomenological presentations. Preliminary categories were formed, uncovering properties and dimensions, and integrating the three. Utilizing cultural characteristics in representative sampling enhances a comprehensive understanding of online learners' characteristics, streamlining subsequent sampling stages.

The researchers will employ a logical deductive-based theoretical sampling approach alongside random sampling for comprehensive comparison and analysis. Theoretical sampling, following a deductive model, involves categories, properties, and dimensions identified through representative sampling that are not saturated. Based on findings and deductions, researchers will establish the theoretical target sampling. For instance, logical deduction of “patterns” suggested conceptual dimensions related to “bidirectional,” leading to the adoption of a theoretical sampling approach to explore specific “bidirectional” patterns, such as the “asynchronous” pattern in online learning. This pattern, identified during representative sampling, involves deeper investigation, and students with limited interactive connections will be purposely selected for interviews. This contributes significantly to refining concepts within theoretical sampling. The research team also conducted random sampling within a sample frame, organizing three focus group interviews to fill gaps in theoretical sampling, test reliability and validity, and assess theoretical saturation robustness through interactive interviews.

After three rounds of data collection and coding analysis, the study formed complete categories, properties, and dimensions. Please see Table 1.

After identifying categories, properties, and dimensions, this study follows The Grounded Theory's storyline organization for core category refinement.

Online learning during the epidemic, a forced adoption, exhibits advantages and disadvantages in college studies due to human-machine-human interaction and spatiotemporal flexibility. Students' motivation depends on self-regulated capacity, influenced by teacher-student interactions, guided by instructors, and the level of self-regulation. External factors (technology and environment) and internal factors (teaching strategies and content) moderate this process. For instance, gamification teaching can engage less self-disciplined students, leading to logical learning satisfaction. Regardless of the engagement mode, students have parallel experiences akin to Schrödinger's Cat, being “logically” dissatisfied but “emotionally” satisfied with e-learning. In summary, online learning's ultimate experiences are shaped by essential psychological needs and rules.

From this, we distill the core categories of this study. The storyline begins with the characteristics of online learning and concludes with the profound experiences it generates. Whether it's students' motivation and engagement levels, or the impact of internal and external interventions, these remain merely “contingent” factors in online learning. The “inevitability” determinants of online learning status lie in internal psychological needs and understanding patterns. Hence, the study identifies “Schrödinger's cat-parallel experiences” as the central category around which all “contingent” and “inevitable” factors revolve.

The coding paradigm model of this storyline is shown in Figure 1.

Research shows that the shift from offline to online significantly changes college students' learning. This is mainly determined by online learning's Human-Computer-Human and Spatiotemporal flexibility characteristics. The so-called online where a screen separates teachers and students, is the opposite of offline, face-to-face teaching. In this learning model, teachers and students can freely talk to each other. However, in the actual situation, the teacher or the students often only output in a “one-direction” way. We rarely turn on the camera. Moreover, when we answer questions, we feel like just talking to ourselves with no one physically in front of us. (F-H-M-230916) Even if there is a two-way interaction between teachers and students, it is mostly lagging and belongs to the “asynchronous” mode. After all, teachers and students are separated, and even in the discussion forum, statements can only be seen after refreshing (the website). (M-SS-O-230918) The freedom to learn at your own pace, the option to stay at home, and the comfortable settings were the most often cited benefits of the Human-Computer-Human mode (Baczek et al., 2021). However, the biggest problem is you cannot see your classmates and do not feel like going to school anymore. (M-S-O-230711) Besides, the online learning atmosphere could be more exciting and take time to adapt. Facing the computer for a long time makes many students feel physically fatigued, decreasing their learning efficiency.

However, the spatiotemporal flexibility of online learning also brings another kind of perception to most students. On the one hand, there is no restriction on location for learning. While most students take classes online at home, others take classes in libraries, cafes, and dormitories. There are no rigid restrictions compared to face-to-face instruction. On the other hand, time is flexible. I can look for information about the teacher's lecture on my computer at any time…The teacher's PowerPoint or recorded video can be accessed again and again. This feeling is different from offline. (F-H-O-231012)

Accordingly, the advantages and disadvantages of online learning constantly interact together and even transform each other. For example, when I was in the dormitory by myself, it was free indeed. However, with computers and cell phones around, it is easy to get distracted during online classes. Unconsciously, I play games or fall asleep. (F-SS-M-230713) The reason for this phenomenon is closely related to the changes that have taken place in learning, which are concentrated in the areas of motivation and interactive connections. This phenomenon occurs because of learning changes focused on motivation and interactive connections.

“Offline” and “online” are seemingly analogous terms; however, from the student's viewpoint, the characteristics of Human-Computer-Human interaction and spatiotemporal flexibility engender significant shifts in the learning paradigm. The category of learning change encompasses two attributes: “motivation” and “interconnection.” The contextual domain is shaped by the amalgamation of various dimensions of these two properties, giving rise to four distinct types of online learning changes for students: Mind-body integrated, Passive regulated, Emotionally comforted, and Self-value added. Please see Figure 2.

Quadrant I combines “strong” interconnection and self-regulatory status “self-discipline”. Students who move to the upper right of this quadrant tend to be more Mind-body integrated. This type of student has clear study goals and a detailed life plan. I need to make a detailed plan for myself every week and organize tasks at each stage. (F-S-O-230916) They not only deeply know the meaning of learning but also can experience the joy of learning. If teachers and students are active enough in their interactive connections, including active discussions, deep thinking, and high levels of participation, it can lead to complete immersion in learning. (F-H-O-230711) Motivation is a topic that many scholars have discussed. Some students enter the classroom with a “motivation to think”. No matter what the teacher does, these students always adjust their mindset to learning. These students fully engage and reflect on their thoughts and actions when the classroom is vivid and exciting. When teachers teach online with more interactions, you will be so eager to share that you will type on the computer and send it up immediately. In offline learning, you will not have this urge. After all, you are too embarrassed to interrupt the teacher's class. (M-SS-O-231012)

Quadrant II combines “strong” interconnection and self-regulatory status “Mind wandering”. Students toward the upper left of this quadrant tend to be passive regulators. In the interviews, a large percentage of the students believed they had low self-discipline. Learning can be affected by mind wandering and attention distracted from a task, especially in increasing online learning environments (Randall et al., 2022). Your brain automatically identifies the home as a place to rest when you take online classes at home, making it difficult to focus on and control your learning. (F-H-M-230920) So, motivating students to learn is much harder if teachers do not shift their offline teaching mode. The teacher ^***has the common touch, teaching knowledge just like telling the story. Also, he constantly sends emoticons and small red flowers. The interaction in the comment section of this teacher's class has been very active since before the class started. (F-H-M-230715) The learning environment partly determines motivation for online learning. In this kind of environment, students' expectations have been lowered. Even when teachers have a strong theoretical capacity and coherent teaching, some students still easily forget the knowledge. However, when teachers can better interact with students and add more practical sessions, students, although in a passive environment, will be positively conditioned by the change in the teacher's interactive approach and practical feedback. I would be touched by the teacher's relaxed yet colorful approach. Even after class, I will reflect and consider how some questions should have been better answered. (M-SS-O-230920)

Quadrant III combines “weak” interconnection and self-regulatory status “Mind wandering”. Students toward the lower left of this quadrant are emotionally comfortable. Traditionally, students are believed to become freeride once these two are combined. However, online education is unique because this group of students is more accustomed to a relaxed, comfortable, and free atmosphere. I did not feel uncomfortable (learning online). Moreover, I was more relaxed than in in-person classes, in which I felt very pressured, especially when answering questions because I felt like I was in the spotlight. (F-SS-M-230713) Other students may think that online learning is more advantageous because they are easily distracted by other things in face-to-face classes. Physically, you have to care about wearing, makeup, arrival time, and even who is sitting around you. Unlike online, you do not have to think about these things at all. (F-SS-O-231012) Even those students who think they have weak self-control want to take advantage of the online time and space flexibility to initiate change themselves. Online classes make me lax, and the professor does not try to create an interactive atmosphere. In order to keep myself from falling too far behind, I need to go online to find some information myself...... (F-SS-M-230918) For this kind of student, the biggest advantage of online classes is that they feel comfortable and do not have the tension they feel when studying offline. This experience can even replace the real purpose of learning.

Quadrant IV combines “weak” interconnection and self-regulatory status “self-discipline”. Students in the lower right of this quadrant tend to be self-value-added. Due to the nature of the online classroom, the interaction could be better. When teachers find that interaction is not very effective, I find that they tend to lecture more. (M-S-O-230718) Self-disciplined students can turn online disadvantages into advantages. The teacher does not clarify it, and constant listening can be exhausting. I would go online to find relevant information on my own and combine it with what seemed uninteresting in the lecture. I would also discover knowledge that I had not known before, which was an exciting process (with an expectant look)........ (M-SS-O-231018) Suppose such a process of knowledge growth is “unintentional” during boring learning. In that case, another group of students has an active self-regulatory strategy and can learn at their own pace. It has been proved that using self-control techniques significantly enhances motivated learning behavior (Pawlak, 2022). Furthermore, self-regulatory structures are thought to be the main elements influencing long-term engagement and academic performance (Sun et al., 2018). I do not require myself to pay full attention in every class. I mainly like online classes because of the opportunity to access class records and playback. When I study via video and playback, I can study at my own pace. I can pause, take notes, and look up information anytime. So I do not care how the teacher teaches, because I study again after the class. (F-H-O-230920) Students with strong self-discipline need the possibility to acquire knowledge and only care if the platform for acquiring knowledge is provided. With strong interactions, students with strong self-discipline are more fully engaged; with weak interactions, students with strong self-discipline look for paths to self-improvement.

In the face of changes in the learning transition process and challenges in students' adaptation levels, students differentiate between rational and emotional engagement. Changes in the level of engagement in response to internal and external conditions manifest this differentiation.

The critical factor determining undergraduates' learning experience is their engagement with learning. The duality of engagement also determines the duality of experience. However, it is paradoxical when focusing on the experience. Students' rational and perceptual responses are a “superposition state” of satisfaction and dissatisfaction. Just like a Schrödinger-cat state, an interesting quantum superposition of classically different states may be deterministically produced by using a single atom in a cavity to regulate a propagating optical pulse (Duan, 2019).

Thinking about online learning logically, the Marginal Effect of the teacher's class is significantly lower. Besides, the content of the class is not consistent with the teacher's expectations. You can clearly feel that teachers teach more things offline compared to online. The teachers also say they cannot expand topics on specific areas and have to skip them. (M-SS-O-230916) Being in the online human-computer environment, it is difficult for the teacher to have emotional connections with classmates, let alone emotional responses needed for the marginal expansion of knowledge. Therefore, the educational content is correspondingly reduced in depth and breadth. In online classes, teachers cannot see our eyes, then they may just follow the routine of teaching. (F-H-O-230715) The root reason for this is that online education's communicative nature is too weak. If teachers could adopt vivid, practical strategies with relatively few external distractions, teachers' knowledge expansion and the marginal benefit to students would be enhanced.

Another rational perspective concerns the difference between learning and learning efficiency. Through the process of coding dimensions, the keyword that can be extracted is “not fully understood”. Students seem to learn the same things as they do offline, but they feel they do not fully understand them. We are not really sure if we have learned anything, even though we have fairly easy access to the online classroom. This situation is more due to the lack of efficiency in the online classroom. Most colleges and universities have adopted flexible assessments due to the shift in teaching mode. However, it has resulted in grades going up, but we learned a little (M-SS-M-231012). Different student types in the four quadrants responded diversely to the learning situation. Nevertheless, all students expressed their dissatisfaction with the level of knowledge acquisition in the online classroom.

Although almost all students expressed rational dissatisfaction, they simultaneously expressed emotional satisfaction without realizing that they were both satisfied and dissatisfied with learning online. Online learning is a thing that makes people feel happy, convenient, free, and comfortable. I can learn anytime,... well, but sometimes it does not. It is cold. I cannot adapt because I hate this process. (F-SS-M-231018) The autonomy and freedom of online learning are perceptual and intuitive experiences. Being unable to adapt or hating is based on rational reflection on knowledge learning. These two seem contradictory, but they can always coexist, just like Schrödinger's Cat's “superposition states”–a parallel experience of the coexistence of sensibility and rationality.

The Grounded Theory's strength lies in the systematic development of a substantive theory through the identification of core categories within the realm of conceptual coding. The primary theoretical contribution of this study is elucidated in Figure 1, which delineates the logical progression of the storyline and the core category of “Schrödinger's Cat's parallel experience.” It is imperative to clarify that, within a specific learning transition context, the study does not seek to construct a theoretical framework. Rather, it aims to deeply attribute the specificity of online learning experiences, employing the logical path inherent to grounded theory. Despite the constancy of essential elements in the learning process—such as teachers, students, learning objectives, knowledge transfer, teaching methodologies, and assessments—alterations in the external environment can induce changes in students' fundamental psychological needs, thereby giving rise to a parallel experiential phenomenon reminiscent of Schrödinger's Cat.

The second theoretical contribution involves refining the scope of implications within the Self-determination theory. Traditionally perceived as a theory of motivation, the Self-determination theory emphasizes autonomy, relatedness, and competence as psychological needs contributing to internalizing extrinsic motivation and fostering optimal experiences that yield a sense of wellbeing and enjoyable performance. However, existing research predominantly focuses on how behavioral and motivational factors predict students' course selection, with limited attention to the impact of the online learning model on psychological needs and subsequent changes in learning perceptions (McPartlan et al., 2021; Zhou et al., 2021). While previous studies have explored the transformation from external to autonomy, the specificity of the online learning model introduces the integrated type, self-value-added type, and regulated type as statuses and learning styles, as illustrated in Figure 5. These, in turn, drive students' rational engagement and learning experiences. In the context of transitioning from offline to online learning, students' engagement and experience result from the combined influence of self-determination and natural determination. Both self and external factors can regulate satisfaction levels of engagement and experience, albeit with a lesser likelihood of transforming the ultimate parallel experience—a key theoretical implication elucidated by this study.

Despite limitations in the online learning experience for undergraduates, enhancing their learning engagement and experience is possible by modifying the moderating effect of external variables.

On the one hand, addressing the weak communication aspects of online learning involves strengthening the development and application of synchronous communication technologies, such as VR, to make interactions more realistic. Technological advancements can significantly regulate students' engagement. In the Human-Computer-Human context, educational institutions should establish effective systems to replicate the in-person learning atmosphere, avoiding alienation of assessment functions, or imposing undue constraints on student learning.

On the other hand, in response to the lack of efficiency in online learning, teachers and students need to improve their digital communication skills for technology-enhanced teaching (Chiu, 2022). Making the Internet a tool for increasing learning efficiency rather than a stumbling block is necessary. In addition, teaching is both a science and an art. A timely shift in pedagogy strategies can often make a significant difference. If you are learning on the Internet, you have to conform to the characteristics of the Internet. For example, teachers could say some popular slang. It will make students feel they are on the Internet, and their interests will follow... (M-H-M-231012) Such as using Kahoot, BLOOKET's website, and doing games or competitions to let students grab or choose answers. The teacher can, at the same time, zoom to implement a classroom quiz. (F-SS-O-231018) On the Internet, popularity surpasses steadfastly reading from a book. Similarly, online learning content should be practical to maximize student learning motivation. Even in theoretical courses, practices must closely relate to open the closed physical environment. This approach allows teachers to vividly expand the scope of knowledge, enhancing the marginal effect of online learning and ensuring students learn what they need to.

The study's primary limitation lies in the sample focus on students from Macau, China, the Mainland, Hong Kong, and Portuguese-speaking countries. While culturally diverse, the findings' generalizability to European and American students is yet to be empirically tested. Considering the influence of different cultures on psychological needs, as emphasized by the self-determination theory (Ryan and Deci, 2020). Future research should explore online learning experiences among students from various cultures to validate this study's findings.

The second limitation is the formulaic nature of the study's dimensional quadrant combinations of motivation and interactivity. These combinations offer a broad categorization of student learning types after a learning change but lack insight into cross-cutting contextual attributes. For instance, the combination of weak interactivity and self-discipline may exhibit characteristics of Mind-body integration along with Self-value added. Future research should focus on specific learning processes, employing detailed and practical classifications with feasible research instruments to portray the characteristics of online student learning vividly and intensively.

In summary, while the human experience is real, the online learning experience resembles a superposition state, distinct from the eigenstate, akin to a quantum phenomenon. Therefore, exploring the feasibility and effectiveness of online learning is crucial, beginning with an examination of the experience. Future studies should uncover the fundamental changes in students' psychological needs that shape the online learning experience, enabling research to better address issues that arise in the teaching and learning process.