Postcards

On Friday, we sent 2 postcards to ourselves from Seattle. We put them in the same mailbox in the hotel. Two days ago, we got one of those postcards (along with one from Ketchikan, Alaska, which, I am happy to say, still uses the postmark stamp instead of running it through one of those computerized machine things), but not the other. We still have not gotten the other. How is that possible? We mailed them at the exact same time!