In fact, it is not that you are stupid, but that you have not found a suitable learning method. Mathematics is actually a step-by-step process. For example, when you first learned 1+ 1 as a child, you must have found it too difficult, but now you must find it the easiest. So you found it difficult when you were a child, which means you are stupid? Of course not. I believe that most children find it difficult when they first start learning.

However, I wonder if you are in high school now. Junior high school? Or?

In your present situation, I think it may be that you didn't lay a good foundation in a certain part before, especially in some small places. At first glance, I don't think it's important, but over time, you may find a lot of details that you can't understand, and the book doesn't explain them very much, and the answers are not listed, but after that, you don't know how it came from. Why do you want to do this, right? If this happens, it may be those details. The screenwriter or teacher thinks that you should have understood these details before, so there is no need to write them. You get it.