who said you cannot step into the same river twice
Heraclitus Heraclitus was famous for his insistence on ever-present change as being the fundamental essence of the universe, as stated in the famous saying, "No man ever steps in the same river twice"[6] (see panta rhei, below). This position was complemented by his stark commitment to a unity of opposites in the world, stating that "the path up and down are one and the same". Through these doctrines Heraclitus characterized all existing entities by pairs of contrary properties, whereby no entity may ever occupy a single state at a single time. This, along with his cryptic utterance that "all entities come to be in accordance with this Logos" (literally, "word", "reason", or "account") has been the subject of numerous interpretations.