The phrase “One cannot step twice in the same river” is one of the most famous metaphors from the ancient Greek philosopher Heraclitus. Heraclitus is known for his doctrine of change being central to the universe.
The statement suggests that everything in the world is constantly changing, and nothing remains the same. Using the metaphor of a river, Heraclitus argues that if you step into a river, step out, and then step back in, it won’t be the same river as before. The water you first stepped into has flowed downstream, and new water has taken its place. In a broader philosophical context, this is Heraclitus’s way of saying that the nature of life itself is change. Nothing remains static or unchanging, and this is a fundamental aspect of the universe.
Just as you can’t step into the same river twice, you can’t live the same moment twice. This idea has had a significant influence on many philosophies and philosophic concepts that deal with change, impermanence, and the nature of existence.