1
general::
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]
American Heritage Idioms
2
general::
Phrase(s): 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.
McGrawhill's American Idioms And Phrasal Verbs