John lives his life by statistics and is afraid to fly. One day his friend, Bill, asks him, "Why do you have this irrational fear of flying?"

"Irrational?" John replies, "Not at all. I've merely calculated the odds of a bomb being placed on a plane and it's much too high for my comfort."

A few days later, Bill boarded a flight only to find John sitting in the seat right next to him.

"What happened? Have the odds changed?"

"No," John replied. "The odds of a bomb being on a plane haven't changed. But I calculated the odd of two bombs being on a plane, and I found those odds much more acceptable. So now I just bring my own."