Live by the harmless untruths that make you brave and kind and healthy and happy.

Vonnegut is urging a pragmatic, humane relationship to belief: some “untruths” (comforting stories, ideals, or self-conceptions) may be factually shaky yet ethically and psychologically beneficial. The key qualifier is “harmless”—the line distinguishes between consoling fictions that foster courage, kindness, health, and happiness, and destructive lies that enable cruelty or denial of responsibility. In Vonnegut’s broader moral outlook, people often need narratives to live by; the measure of a narrative is less its metaphysical certainty than its effects on human flourishing. The quote thus reads as a compact defense of benign illusion and a warning to judge beliefs by the good they do.