Section 146 of Jenseits von Gut und Böse is twenty-eight words in the German. Wer mit Ungeheuern kämpft, mag zusehn, dass er nicht dabei zum Ungeheuer wird. Und wenn du lange in einen Abgrund blickst, blickt der Abgrund auch in dich hinein. Whoever fights with monsters should see to it that he does not become a monster in the process. And when you stare long into an abyss, the abyss also stares back into you. The aphorism appears in the chapter Nietzsche titled Sprüche und Zwischenspiele, interludes and proverbs, where he is testing the compression of his ideas to their smallest workable form.
The compression matters. §146 carries, in a single complex sentence, the same problem the surrounding chapters of Beyond Good and Evil unfold over hundreds of pages: that the will to oppose evil and the will to power are not separate motions, and that conviction earned in struggle is contaminated by what the struggle required. Nietzsche is naming what Adorno would later call the dialectic of enlightenment: that any project pursued long enough becomes susceptible to becoming its opposite.
The line about the abyss has had a longer afterlife than most of Nietzsche's longer arguments. It now sits in commonplace quotation alongside Shakespeare and Marcus Aurelius, often without attribution, often softened by translation. Most of the soft readings turn it into a warning about depression: do not look at dark things, they will make you dark. Nietzsche meant the opposite. The warning is about righteousness. The person fighting monsters with absolute certainty is the person most at risk of becoming one. The abyss is not the enemy. The hardened gaze is.
