In fact, there were many cases where I didn't clearly understand the concepts of Spring DI, AOP, IOC, etc. or the structure of the JVM when I read various blog posts. Since I didn't understand the principles of the technologies, I naturally just memorized the technologies, and even that would be forgotten over time and I would wonder, "What was it?" I happened to watch this lecture while preparing for a job change, and since I was able to understand the principles of the technologies that I had been using without thinking, I felt like I understood them a little more clearly. If I listen to the same lecture a few more times, I think I will think more deeply and understand more deeply whatever I read. Also, although it is knowledge that may disappear due to volatility, I think it is different from knowing the principle of whether something works or not, so it was a really meaningful lecture for me.