Whoever Fights Monsters Should See To

From Beyond Good and Evil (1886), Chapter IV ("Maxims and Interludes"), Aphorism 146. The two-sentence aphorism is a single continuous thought: the warning against becoming a monster is immediately followed by the abyss image, suggesting that the corruption happens through prolonged, obsessive engagement rather than a single act. Nietzsche situates it within a broader critique of morality rooted in ressentiment — the tendency of those who fight evil to define themselves entirely by their enemy and, over time, to adopt the enemy's methods. Carl Jung later developed a related concept he called enantiodromia, the psychological tendency of an extreme position to flip into its opposite.