The past and the future belong to the relationship of time. Don't think that you can rely on your intelligence to cross the long river of time. Cause and effect, you know, even very close people may not be able to get together again.

This couplet belongs to the dreamland dreamt by Jia Baoyu in A Dream of Red Mansions.

If we simply appreciate the original text literally, we can say that the first sentence is an understanding of time, and no matter how clever a sage is, he can't cross the long river of time. The second sentence is a causal relationship. When the cause and effect are mature, there will not be too many implications because of the relationship between people. Moreover, there is a kind of causal conceit, even if it is a father and son, it can't replace each other's truth.