A parent decreed one Christmas that she was no longer going to remind her children of their thank-you note duties. As a result their grandmother never received acknowledgments of the generous checks she had given. The next year things were different, however. "The children came over in person to thank me," the grandparent told a friend triumphantly. "How wonderful!" the friend exclaimed. "What do you think caused the change in behavior?" "Oh, that's easy," the grandmother replied. "This year I didn't sign the checks."