After wandering around in front-end, infrastructure, and back-end for a long time, I found the most interest in back-end and decided to pursue a career as a back-end developer. While listening to Younghan's lectures, I realized I hadn't truly experienced anything in depth. It seems I focused more on how to implement features, prioritizing quantity over quality, rather than on how to effectively utilize the materials involved in building something. While the depth of content in the lectures is excellent, the final problem truly seemed to be a task that provided insight into "Object-Oriented Programming." When I first tried to solve it, I naturally approached it in a procedural manner. It felt somewhat like hardcoding, so I tried refactoring it myself, but I couldn't follow the code provided in the problem solution. That problem was truly great. I learned a lot. Actually, I had a rough understanding of the Collections Framework while learning data structures, but after seeing concurrent collections in the advanced section, I felt I needed to review them and did so. I realized again that my understanding was insufficient... Even after watching this lecture, I think it's a topic that I'll need to revisit continually, even beyond this course. This is my first time leaving a review for Younghan's lecture, but thanks to Younghan, I truly came to like Java. Thank you!