I understood it after four times. I recommend that you study on your own while taking the lectures. After studying on your own - especially the concept part - to raise your level, I think I'm progressing quickly when I listen to Younghan's lectures. I've purchased three more lectures on JPA map and Spring map, and I'm going to become a proper server developer. Complete one lecture at a time and don't skip right away, but look at the code and recall what you did!