Heraclitus said....

"No man ever steps in the same river twice, for it's not the same river and he's not the same man."

Heraclitus of Ephesus was a Greek philosopher (535-475 BC). He is famous for his insistence on ever-present change in the universe - as in this quote.

He had a good number of other memorable things to say. I like this one...

"Hide our ignorance as we will, an evening of wine soon reveals it." (Pub quizzers beware!)