We believe no evil till the evil’s done.

The line expresses a common human tendency toward complacency and denial: people often refuse to credit warnings, suspicions, or signs of danger until harm has already occurred. It points to the psychological comfort of assuming the best—and the social cost of that assumption when it delays prudent action. In a La Fontaine context (even when filtered through later translation), the sentiment fits the moral logic of many fables: characters ignore evidence, trust appearances, or dismiss counsel, and only “believe” in the threat once consequences make it undeniable. The aphorism thus functions as a caution against naïveté and as an argument for foresight, vigilance, and taking credible risks seriously before they become irreversible facts.