Who is to determine what the perfect is? It could only be those who are themselves perfect and who therefore know what it means. Here yawns the abyss of that circularity in which the whole of human Dasein moves. What health is, only the healthy can say. Yet healthfulness is measured according to the essential starting point of health. What truth is, only one who is truthful can discern; but the one who is truthful is determined according to the essential starting point of truth.

p. 127 - Nietzsche (1961)