It is very simple, because it can roughly summarize a person's life through the date of birth and see the future through the present situation. This is academic, not superstitious. So some people say it's superstition, because many people cheat under the guise of eight characters.
Let me give you an example. If you can see from the eight characters that a person will open a restaurant or work in a cookhouse squad in ten years, in fact, he doesn't open a restaurant now. But you don't tell this person what he will be like, so if you can find this person in ten years, he is probably opening a restaurant. This is what the eight characters can do.
In fact, I don't advocate widely publicizing this academic topic, because fate always exists, not for Yao's survival or Shun's death. Spying on justice will be punished, and fate should lead a wonderful life.