OK, maybe some very smart guy can enlighten me but I really do not understand why Codegym asks for using the Note class as lock (or the list or even any object that I create for just that locking purpose, that all should have the same result). Why not just using this as lock. That current code would not need more? If the list and the two methods (addNote, removeNore) were static, then I could understand it without any problem. Or if at least the list was static. Then one could argue that all Note objects modify the same container. Accesses to this would have to be protected. But here we even have instance methods. And each instance has its own list. Therefore it should be sufficient to synchronize this. Am I missing something or is there simply no reason for this requirement. I'm going crazy, totally crazy.... crazy 🤪😜 Thank you very much my dear fellow learners. oh, and it's that task: Link to english version of 1703