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To be aware or capable of better or smarter behavior than one has demonstrated. You know better than to talk to strangers! What were you thinking? You know better than to try to question that professor—he doesn't care what we have to say.
know better (than to do something)
to be wise enough, experienced enough, or well trained enough not to have done something wrong. Mary should have known better than to accept a lift from a stranger. Children should know better than to play in the road.
Be able to recognize something as wrong or not possible, as in Mary should know better than to leave her child alone in the house, or Try to get in without a ticket? You know better than that. [c. 1700]
know better thanbe wise, well-informed, or well-mannered enough to avoid doing something specified.
1989 Anne Fine Goggle-Eyes Inspector McGee knows better than to tangle with Beth's granny.