I got completely blank postcards identical on both sides and requiring a stamp as they were not postage paid. I put the same message on both sides that said:

“You have recieved the notorious Postmaster’s Choice. On the opposite side of this card is an identical message addressed to someone else. This message got to you because whoever sorted the mail either saw the side with your address first or thought you would be a more worthy recipient for some unknown reason. There really isn’t any logic to this. The postcard may have just as well been thrown out as undeliverable, but it wasn’t.
Random chance has given you something. At the least it is something amusing to tell friends and neighbors. At most it could show you the beauty of chaos so that you may submit to it and in turn control it.

Sincerely,
Scooter.”