Elementary mathematics can be understood as some simple concepts. If you understand these concepts and know how to use those formulas, there is basically no problem. Whether it is space geometry or plane geometry, function or other operations, it can be completed without abstract thinking, and the requirements for abstraction and speculation of thinking are not high. Therefore, elementary mathematics will be slowly explained in junior high school and senior high school until the university. It has a certain connection with human elementary mathematics, but it is not so close.
Advanced mathematics pays great attention to thinking, which is the change of your thinking habits. I can't memorize formulas and theorems mechanically like elementary mathematics, so I can't do problems. Advanced mathematics pays great attention to skills and feelings. It can be said that all the exercises and classes we do are aimed at finding this feeling. As soon as we saw this problem, we knew how to solve it. This feeling has formed advanced mathematics. Basically, it includes the series of extreme calculus and so on, and the course is subdivided into many kinds. The most important thing is calculus, because it is the pillar of higher mathematics and the most abstract and interesting thing.
Learning calculus is a painful process, because many of its concepts are abstract, especially when learning multiple integrals. He can only convey this idea through dictation, which is simple to understand, but there is no way to understand it. Because it is a very abstract concept that you can't draw with strokes, the study of advanced mathematics is doomed to be difficult.