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]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.