本句出自尼采的Jenseits von Gut und Böse（Beyond Good and Evil,《善与恶的超越》）（1886）。
原文是德文：
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.
英文译本有：
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.
He who fights with monsters should be
careful lest he thereby become a monster. And if thou gaze long into an abyss,
the abyss will also gaze into thee.
Beware that, when fighting monsters, you yourself do not become a
monster... for when you gaze long into the abyss, the abyss gazes also into
you.
中文释义：恶龙之所以为恶龙，是因为他的行为冲破道德底线、正义原则。这些会让他的进攻更加无所顾忌，更加凶狠毒辣。我们要想战胜恶龙，很多时候必须也使用恶龙的毒辣手段，时间长了，即使我们胜利了，我们也在一定程度上变成自己最讨厌的那种人。
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