I had a lot of trouble when I applied a newly learned feature to a personal project, thinking, "Oh, it works!", but it didn't work as I thought. I think that you need to understand the basic principles so that you can list the causes of problems that may arise later and fix them one by one. (Of course, as you said, there are too many to learn and understand all the principles...) Since you explained the core principles and the reasons for various situations together, I was able to think a lot on my own and felt like I was saving time. Thank you always!