The topic is good. I bought it because I was attracted by the topic... After listening to it all, I think it's expensive compared to the depth of the content and the quality of the lecture. It was about 20,000 won, so I bought it with the intention of treating my colleagues to a nice meal and listening to their stories, but it would have been nice if it had been just a cup of coffee. First of all, the text is too small. It's too small. I think they only thought about people with large screens or such environments, but maybe they didn't think about it at all. It's too hard to look at on a 15-inch laptop. When the lecture starts and I try to follow along, it's hard to read the text on the screen, so I feel bad and want to stop listening to the lecture... And the explanations for each lock in the middle seem too simple. After listening to it, I think the tuition fee felt more expensive because I already knew everything. Also, when creating a facade instead of a service, it would be good if you could tell me why you use a facade instead of a service interface or class. Lastly, starting with NamedLock, none of the test cases work... The environment is the same and the code is the same, so why doesn't it work? Even when I downloaded the lecture source from github and ran it, it didn't work, so I just stopped learning.