When you've decided you want to decrease the number of Christmas cards you send out every year, so you decide to send cards only to people who send you one first. However, this can backfire if someone on your potential list is using the same tactics. This results in a standoff and ultimately no card exchange between the two of you. This does help solve the original problem, though.
I decided to play Christmas Card Chicken with my second cousin Jennifer, because I didn't want to waste a stamp on her unless I get a card from her first. However, I haven't gotten one from her, so she's probably waiting to get one from me first. I guess we can just be facebook friends instead.