The core of the problem is theorem and definition. The people who can give questions are not ordinary people. They know the ins and outs of the theorem definition, and set up several levels through reverse thinking to get you stuck.

If you are a student, you only need to know the purpose of the question, and you don't need to know how to create it. Now the teacher writes two questions or changes them on the blackboard casually, because they have done too many questions. They don't have that ability at all. As a student, don't be hard on yourself, focus on the cutting edge, ok.

If you really want to know, go to the blog of Science Network and ask some famous mathematicians for advice. Only they can satisfy you, but I can't satisfy you. Um ... .