EpilogueIt has been more than 20 years since the HCI Lab at Yonsei University was founded. There has been a dramatic change in our surroundings over the last 20 years. The internet has become an inseparable part of our lives, and smartphones are now more important than PCs. I expect the changes in the next 20 years to be just as dramatic in speed and scale, if not more.The HCI Lab has been, and still is, working extremely hard on its researches. We participate in numerous government-funded research projects, and we work together with the industry to seek solutions to its problems. I have been highly motivated to teach courses at the university, thanks to the wonderful students who have showed their diligence and enthusiasm towards the field of HCI. We work hard to develop the ideas that are brought up during classes and projects into research papers.Yet sometimes, I feel like something is missing. Even great research papers become outdated in few years. This is especially true for HCI papers that are based on trendy IT technologies in this fast-paced world. In reality, journal papers in HCI field easily fall behind the trends during its review period.So I began to think that we need to understand the fundamental principles in the field of HCI in order to devise design principles and processes that can last for decades. Moreover, it is more important to understand "why" than "how." So I initially began putting down my thoughts on my daily experiences with various IT products and services in small hopes of finding out the "why."But the small hopes grew larger during the process of writing. As a president of the Korean HCI Society, I became ambitious to let the world know of the excellence of the HCI community in Korea. I also felt responsibility as a General Conference Chair of the organizing committee for the ACM SIGCHI conference, which is held in Korea for the first time in 2015. While writing, I was also appointed as Vice President of the Library and Information Services of Yonsei University.However, such big hopes and ambitions were more of a hindrance than help for my writing as I became too stressed out and pressured to enjoy the process of the writing itself. I even thought about deserting the writing completely.