People can't step into the same river twice. "This is a philosophical theory, that is to say, things are constantly changing and absolutely moving. Therefore, when you step into the same river for the second time, it has changed, and it is no longer the previous one.

"People can't step into the same river once" is a sophistry of the above view. He thinks that when you cross the river, the river is changing, so you can't step into the same river once. This view denies that the object is relatively static, which is a wrong view.