While working without much knowledge, I've now returned to the beginning to re-establish concepts from the ground up. As I listened, I reflected on why I used to write things the way I did – code that was worse than even the example code and had no OCP applied whatsoever, all because I was in a hurry, before Younghan-nim improved the practice problems. I'm relieved that I can finally re-establish these concepts, and thank you for creating such a great lecture.