Tell me an example of a proof question~ When most people encounter difficult proof problems, they usually cannot directly see through the proof process from known conditions to results at a glance. In the case of a certain foundation, it is generally done according to a certain routine first and keep trying. It may prove that there is no clue for a while (if you don't do it, you will never have a clue); It may also be "the mountains and rivers are doubtful and there is no way, and the willows are dark and the flowers are bright and another village". The same is true for investing in many times.