„He who fights too long against dragons becomes a dragon himself; and if you gaze too long into the abyss, the abyss will gaze into you.“
— Friedrich Nietzsche, livro Para Além do Bem e do Mal
Beyond Good and Evil, Aphorism 146
Variante: He who fights with monsters should look to it that he himself does not become a monster. And if you gaze long into an abyss, the abyss also gazes into you.