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Phrase(s): Ignorance is bliss.
Prov. Not knowing is better than knowing and worrying. • A: I never knew that the kid who mows our lawn has been in trouble with the police. B: Ignorance is bliss!
McGrawhill's American Idioms And Phrasal Verbs
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What you don't know won't hurt you. For example, She decided not to read the critics' reviews? ignorance is bliss. Although its truth may be dubious at best, this idea has been expressed since ancient times. The actual wording, however, comes from Thomas Gray's poem, "Ode on a Distant Prospect of Eton College" (1742): "Where ignorance is bliss, ‘tis folly to be wise."
American Heritage Idioms