To know which side your bread is buttered on is an idiom that goes back at least to the mid-1500s. An idiom is a word, group of words or phrase that has a figurative meaning that is not easily deduced from its literal definition. We will examine the definition of the phrase know which side your bread is buttered on, where it came from and some examples of its use in sentences.
To know which side your bread is buttered on means to understand what is to your benefit, to understand where to put your energies in order to benefit yourself, to know which choice is to your advantage, to understand who will be helpful to you. This alludes to the fact that the part of the bread with the butter on it is more valuable. The idiom know which side your bread is buttered on was first recorded in John Heywood’s Proverbs, published in 1546: “I knowe on whiche syde my breade is buttred.” Related phrases are knows which side his bread is buttered on, knew which side his bread was buttered on, knowing which side your bread is buttered on.
Examples:
It’s always important to know which side your bread is buttered on and the Liquid Mechanics Brewing Co. seems to know exactly where that is. (Boulder Weekly)
Democratic demographer Ruy Teixeira has a more prosaic explanation: “Not only are the police likely to vote Republican but the union is the mechanism to mobilize them… It’s about knowing which side your bread is buttered on.” (The Week Magazine)
“On average I’d say I win 25-30 of those matches,” he says with a smile that indicates he knows which side his bread is buttered on. (The New Zealand Herald)