A mother decided one Christmas that she wasn't going to remind her kids any longer of their need to write thank-you notes.

The result of this was that their Grandpa never received any thank-yous for the very generous checks he'd written to the kids. However, the following year, things were different.

"All the Kids came over personally to thank me" said the Grandpa in a triumphant manner...

"That's great," said his friend, "why do you think they decided to change their behaviour?"

"Well, that's easy," declared Grandpa, "this year I didn't sign the checks..."