What I felt after listening to the previous Spring Core Principles lecture and this lecture was that the lecturer did not just explain the concepts but also captured the flow well. It was really easy to understand because he explained the cause-and-effect relationship, such as why this technology should be used and what the limitations were before using this technology, rather than simply saying that this technology exists. In particular, since I was a test taker, I studied while constantly thinking, "Why?", and I think Younghan also thought the same, and the lecture was conducted in the flow of "Why?", "How?", so I personally found it really fun to listen to. And because he lectures in a flow-oriented way, I think that reviewing is even more important. In the lecture, I learned in the flow of A->B->C, but during the review process, I reviewed by looking only at A and thinking about the flow from B->C, or thinking about whether I could utilize the content of D that I learned in other parts. I think this process was a great help in understanding and memorizing the concepts.