Direct self-observation is not necessarily sufficient for us to know ourselves: we need history, for the past flows on within us in a hundred waves; indeed, we ourselves are nothing but that which at every moment we experience of this continual flowing. Even here, when we want to step down into the flow of what appears to be our ownmost and most personal being, the dictum of Heraclitus is valid: one does not step twice into the same river.

Nietzsche, Human All Too Human