The lady in the mcdonalds drive thru gave me too much change but I am not going to say anything.
That's not nice. Why would you hide that?
I want to keep that money.
You really should return that money. It's not yours and you shouldn't lie.
So I should give the money back so you feel better.
No you should do it because it is the right thing to do. She might get in trouble for giving out too much change and get fired, so it is good to return the money when you get too much change.