know on what side one's bread is buttered

Verb

know which side one's bread is buttered on (third-person singular simple present knows which side one's bread is buttered on, present participle knowing which side one's bread is buttered on, simple past knew which side one's bread was buttered on or knew which side one's bread is buttered on, past participle known which side one's bread was buttered on or known which side one's bread is buttered on)

1. (idiomatic) To be aware of where one's interests lie in a situation.
   • They are all stupid when they are not crafty, and very few of them are crafty. The only wise Republicans are the millionnaires and their conscious henchmen. They know which side their bread is buttered on, and they know why.1908 September – 1909 September, Jack London, chapter XXIX, in Martin Eden, New York, N.Y.: The Macmillan Company, published September 1909, →OCLC, page 258