If you owe your brother five bucks, and he says, nah, don't worry about it, keep it?
That is mercy.
If a mugger gives you back five bucks from your wallet, for subway fare so you're not stranded in the bad part of town where he robbed you?
If I hand in my term paper the day after it was due and the teacher accepts it anyway?
If I hand it in apologetically and he asks, what are you talking about? the deadline isn't till next week...?
If a deadly virus is spreading, and the nurse gives a child the last vaccine, which should have been for her, that is mercy.
If the nurse forgoes vaccinating the child because the little one cries, afraid it will hurt?
If a mentor supervises her protege over and over, however many times it takes, to impart a knowledge or skill before he retires, that is mercy.
If a mentor cleans up her protege's messes over and over, and retires leaving the protege at the mercy of his own ignorance and incompetence?
Mercy is a grace, is it not? a share in something good, something of value, to which one is not entitled.
If it should have been yours all along, how is that mercy?
But worse, if despite seeming pretty or shiny or tasty or fun it leaves you worse off than before, how is that mercy?