noun
the quality or state of being foolish; lack of good sense or judgment
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The decision to invest all his savings in a risky venture showed his foolishness.
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Her foolishness in believing everything she read online led to many mistakes.
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I can't believe the level of foolishness he displayed by trying to jump off the roof.
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The foolishness of trying to control everything in life became clear to her as she learned to let go.