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general::
Phrase(s): What you don’t know won’t hurt you. [and] What you don’t know can’t hurt you.
Prov. If you do not know about a problem or a misdeed, you will not be able to make yourself unhappy by worrying about it. (Often used to justify not telling someone about a problem or misdeed.) • Ellen: What a beautiful diamond necklace! Thank you! But how on earth did you get the money to pay for it? Fred: What you don’t know won’t hurt you.
McGrawhill's American Idioms And Phrasal Verbs