mind one's own business

To not interfere in someone else's affairs; to not pry or be nosy. Often used as an imperative. Mind your own business, will you? I can take care of my problems just fine. I really wish she would mind her own business and stop asking me about my finances. So there I was, minding my own business, when the security guard comes over and starts asking me all kinds of questions.

Keep from meddling, pay attention to one's own affairs, as in If she would only mind her own business, there would be a lot fewer family quarrels. Already described as a wise course by the ancients (Seneca had it as Semper meum negotium ago, "I always mind my own business"), this precept has been repeated in English since about 1600.

To refrain from meddling, to keep to one’s own affairs. The wisdom of this course of action was observed in ancient times by Plato, Seneca, and others, and even found expression in the Bible (1 Thessalonians 4:11, “Do your own business”). In plain English it was expressed from the sixteenth century on. John Clarke used it in Paroemiologia (1639): “Mind your business.” Among many later writers echoing this sentiment was Lewis Carroll, in one of his enjoyable non sequiturs (Alice’s Adventures in Wonderland, 1865), “‘If everybody minded their business,’ the Duchess said in a hoarse growl, ‘the world would go round a great deal faster than it does.’”