If you stare into the Abyss long enough the Abyss stares back at you.

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.

When you look into an abyss, the abyss also looks into you.

Whoever is related to me in the height of his aspirations will experience veritable ecstasies of learning; for I come from heights that no bird ever reached in its flight, I know abysses into which no foot ever strayed.

If you gaze long into an abyss, the abyss will gaze back into you.

Battle not with monsters lest ye become a monster and if you gaze into the abyss the abyss gazes into you.