A building contractor was being paid by the week for a
job that was likely to stretch over several months.
He approached the owner of the property and held up the
check he'd been given. "This is two hundred dollars less
than we agreed on," he said.
"I know," the owner said, "But last week I overpaid you
two hundred dollars, and you never complained."
The contractor said, "Well, I don't mind an occasional
mistake. But when it gets to be a habit, I feel I have
to call it to your attention."