This lecture explains the architecture and very basic contents of Spring Security well. But it is true that there are many shortcomings. In fact, I don't know why the reviews are so good. The reasons I think so are as follows. 1. Since the architecture is explained only with debug and code, it is difficult for people who do not have a picture of the overall architecture in their heads to understand. A diagrammatic document is not as good as a well-organized blog. And when explaining the flow, I think you should draw a picture in advance or use a drawing program or tablet to explain it. That is because it is much easier to understand than just looking at the code. 2. The depth of the content is too basic. The reason is that they usually say that there are too many methods because they are afraid that the lecture will be too long, but I think they are targeting people who do not study hard because they are too downwardly leveled. This may be a guess, but even if it is true, there are too few use cases and they only teach very basic contents. 3. It is very common for the flow to be interrupted in the middle of a lecture. There are many cases where the flow is interrupted in a lecture that is less than 10 minutes long, so it makes me feel like I am not prepared for explaining something. - ps. I am currently taking AI and paid math classes for AI study, so I evaluated them with strict standards because they are very serious and well-prepared. I thought a lot about whether or not to say this because I was afraid that you might misunderstand, but I thought you might think I am leaving a bad review because of this part.. But I have to leave it. I was honestly a little disappointed when someone who always values testing asked a question, but he just looked at the documentation without checking the test and Spring code, and assumed that it would be like that.