What Goes Around, Comes Around

DEFINITION: This idiom is used to express a situation in which a person's behavior (either positive or negative) later returns to either harm or benefit him or her.

EXAMPLE: Kevin is such a pleasant person and genuinely cares about his friends. I'm not surprised that so many people donated money to cover his medical expenses - what goes around, comes around!

I don't understand why Steve is so mad that his girlfriend lied - after all, what goes around, comes around!