When I speak of the banality of evil, I do so only on the strictly factual level, pointing to a phenomenon which stared one in the face at the trial. Eichmann was not Iago and not Macbeth, and nothing would have been farther from his mind than to determine with Richard III “to prove a villain.” Except for an extraordinary diligence in looking out for his personal advancement, he had no motives at all. And this diligence in itself was in no way criminal; he certainly would never have murdered his superior in order to inherit his post. He merely, to put the matter colloquially, never realized what he was doing.

Hannah Arendt (1906-1975) German-American philosopher, political theorist

Eichmann in Jerusalem: A Report on the Banality of Evil, Postscript (1963)
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