I used to use Spring Boot a while ago, and I didn't know the principles, but I just wanted to develop it. As time went by, I quickly forgot how I used the technology. As I listened to Professor Kim Young-han's lecture, he explained all the principles I had missed in detail, so this time I remembered them for a long time, and even when I developed using a framework other than Spring, I understood why I developed it that way at the time and it was very helpful. I'm grateful that you've filled in the gaps that I couldn't fill by searching the internet or even using ChatGPT while developing alone through this lecture :D