This is the intuitive perception of Heraclitus; there is no thing of which we may say, "it is." He rejects Being. He knows only Becoming, the flowing. He considers belief in something persistent as error and foolishness.

To this he adds this thought: that which becomes is one thing in eternal transformation, and the law of this eternal transformation, the Logos in all things, is precisely this One--fire.

Nietzsche | The Pre-Platonic Philosophers | "Heraclitus"