Extreme foolishness; the quality of being stupid and lacking intelligence or good sense, often while remaining self-assured.
From Latin 'fatuitas' (foolishness, from 'fatuus' meaning foolish, insipid), entering English through Old French.
Fatuity appears frequently in classic literature (especially Jane Austen) to describe characters who are confidently, completely wrong about everything—it's the foolishness of not knowing you're foolish.
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