I don't even bother to write comments on the internet, but after listening to Younghan's lecture, I am writing a review for the first time in my life! I closed the 'Write a review' window that appears during the lecture and waited until the end of the lecture to write one after listening to the lecture. The lecture was really fun to listen to. It took longer than I thought because I had to reread the PDF for things I didn't know and listen to the lecture again, but I followed along and understood it step by step. I am still lacking in many ways, but I understood it when I wrote the code. The PDF was written in detail with the code, so it was really good to read!! The lecture's delivery is really the best. I didn't regret spending money at all!! I was a fool, but now I am a fool~ I am still a beginner, so I am not familiar with object-oriented principles such as OCP and DIP, so I could clearly see that this part is emphasized because you repeated it a lot. If you hadn't repeated it, I knew it was important, but I almost passed it by without even knowing that you were emphasizing it.... I will listen to all the next lectures and leave a review. I will continue to listen to Younghan's lectures and bow to Baemin headquarters once. Thank youㅎㅎ