Discourse on the Method (of rightly conducting one’s reason and seeking the truth in the sciences)

Heraclitus says, as though he had achieved something great and noble,

I inquired into myself

—Plutarch, Against Colotes, 1118C

Heidegger, writing about just this sort of thing, says

What then was wrested from phenomena by the highest exertion of thought, albeit in fragments and first beginnings, has long since been trivialized.

—Being and Time, 2