People seem surprised when I call them and tell them they've forgotten to bill us for something. Or bring it to their attention when they've undercharged me or given me too much change.
If I want to live in a fair and just world, then I must act in a fair and just manner. Even if it's to my personal disadvantage.
Maybe it's just the accountant in me. I would like to think that, at the end of the day, all columns are added correctly, and everything is in balance.