In fact, when thinking about this problem, most of them are at a time when they have nothing to do. I am so busy that I have no time to think about this problem. If you don't understand, let it go. It is a kind of wisdom to let go. If you don't understand and don't put it down, you will be entangled, just like a fish that gets into layers of fishing nets, and the more you struggle, the more you can't get out.