4PHRASE [Vs inflect]明白自己的利益所在;善于为自己打算 If you say that someone knows what side their bread is buttered on, you mean that they know what to do or who to please in order to stay in a good situation or to avoid a bad one. 明白自己的利益所在;善于为自己打算
These chaps know what side their bread's buttered on.