Congratulations on your signing out. I can totally relate because it's not easy being a student. There are some courses that are very interesting and easy to understand, and there are others that are just the opposite. It has happened to me a lot, especially during exam periods. Sometimes when I’m trying to understand a particular course and I see that it’s not entering my head, I just leave the book and focus on the one I know. I give my best during the exam and use my own English to explain the one I don't know. After the exam, I will just let out a loud sigh, just like you mentioned 😅.