know which side of one's bread is buttered

Idioms

Be aware of where one's best interests lie, as in Jerry always helps out his boss; he knows which side of his bread is buttered. This expression alludes to the more favorable, or buttered, side of bread and has been used metaphorically since the early 1500s.

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023