One cannot step into the same river twice. Heraclitus was a famous master of dialectics in ancient Greece. He has a famous saying: "People can't step into the same river twice", which profoundly and vividly illustrates the idea of the movement and development of things. There was a student in Heraclitus named Kratylos, who went further than the teacher and declared that "one can't step into the same river once". People said to Kratylos, "The river is like this, and so are other things?" Kratylos said proudly, "I am a philosopher. Philosophers talk about the universality of the world. Since everything is flowing and everything is changing, the' everything' mentioned here is of course effective for everything. " Kratylos replied without thinking, "From a philosophical point of view, there is no doubt about it. Everything in the world is constantly changing like this. " Kratylos casually replied, "It's a chair." Kratylos felt that he had been teased. But he still stubbornly stuck to his point of view. Later, he was afraid of making a fool of himself again and shook his thumb at everyone. I can't say the question you asked, just like the shaking of my fingers, everything is changing, and we can't know everything, because it has changed before we realize it. We can't say anything, because this thing doesn't exist before we live. In this way, Kratylos turned to sophistry and denied the relative stability of things. It is said that when a writer learned Kratylos's idea, he created a comedy and invited Kratylos to watch it. It is said in the play that a Greek borrowed a sum of money from a friend and vowed to pay it back in January. But I don't want to return it then. Because he paid the tuition and worshipped a teacher to study philosophy. According to the teacher, everything is changing. People can't even step into the same river once, let alone borrow money for a month. Now he is not the man he used to be. My friend was very angry and caught the Greek and beat him up. The Greeks went to court and demanded compensation for losses and medical expenses. In court, my friend confessed the whole story and finally said, "I know it's illegal to hit people, but now I'm not hitting people, and I'm not myself when I hit people." So, just as he didn't pay me back, I'm not responsible now. At the end of the play, the audience burst into laughter. Someone in the audience recognized Kratylos sitting in the audience. "Look, the teacher who refuses to pay tuition is this Mr. Kratylos! "Kratylos panicked and stretched out his hand and shook his thumb in the past. His behavior made everyone laugh their heads off. The comedy ended in laughter.