Why you step in the same river twice?

You cannot step into the same river twice. Heraclitus, a Greek philosopher, said that. The idea behind it is that the river is constantly changing, with new water flowing in, and new water flowing out, so the river you stepped into a moment ago is no longer the same river. This can be applied to life in general, as things are always changing, and we can never truly go back to the same moment or experience twice.