There are many advantages to the teacher's lectures, but the biggest ones are 1. storytelling and 2. natural understanding. I liked the storytelling and explanation that gradually developed from bad code (messy?) to commonly well-refactored code, and the natural understanding that came from it. When I learned Java before, it was hard because it was broken up into concepts and learned one by one, but when I watched Kim Young-han's lecture, I naturally understood everything without having to memorize it, so the polymorphism part felt very easy. (I don't know if it was easy because I studied in advance.) Now I'm moving on to the intermediate level. Thank you!