I like to consider only one aspect when doing math problems recently, and I don't consider other aspects. For example, Pythagorean theorem, I only want Pythagorean theorem when I do geometry problems, unlike other aspects. What should I do?

This shows that you don't study hard at ordinary times, and you will forget your previous knowledge when you study in a place. Remember, the previous knowledge can be vague and can't be thought of instantly, but the method of doing the problem and the chunks of previous knowledge can't be forgotten.

For example, after you learn Pythagorean theorem, you only need to remember Pythagorean theorem in the future, so that you can think of Pythagorean theorem when you do the problem. What you lack is the memory of the general outline of knowledge.

You think, if someone tells you that this problem can be solved with so-and-so knowledge, then you will. Now just look at the textbook catalogue and remember the knowledge points.

In addition, you are summing up the method of doing the problem. There are actually several kinds. Just think about it and be happy.