The sentence "Children are not fish, how can you know the happiness of fish" originally has three meanings. It can be simply understood that different species can't communicate with each other, and there is no way to exchange feelings with each other, just because vegetables and radishes have their own advantages and it is difficult to force them. Of course, that is to say, fish has the happiness of fish, and you have your sadness. The ancients said that this sentence used homophonic words, so it became "the son is not redundant, how to know the joy of surplus." You can't fully understand, so your sadness and your happiness belong to you, and others can't take them away. For example, my own meaning is not quite the same as that of the ancients. I sometimes feel that if I am not insane, I must be stupid, because a comfortable and happy lifestyle is as unbearable as poison to me in the eyes of ordinary people, and the only thing I can enjoy to the extreme is work. Because only these two things can completely occupy my mind and make me forget both things, which seems stupid to me, but it is really hard for ordinary people to accept. So, "I am not stupid, how can I know the happiness of a fool?"