Wiktionary
mind one's own business
vb. (context idiomatic English) To concern oneself only with what is of interest to oneself and not interfere in the affairs of others.
Usage examples of "mind one's own business".
There would have been no Furies for Oedipus, no disaster for Othello, Romeo, Pericles of Tyre, Laon and Cythna, if it were only agreed to let sleeping dogs lie, and mind one's own business.
For a moment he thought of leaving it there, with the big-city temptation to mind one's own business even when to do so would be an atrocity.