[Steve]

I have a friend who filled his car with gas at a self-service gas station. After he had paid and driven away, he realized that he had left the gas cap on top of his car. He stopped and looked and, sure enough, it was lost.

Well, he thought for a second and realized that other people must have done the same thing, and that it was worth going back to look by the side of the road since even if he couldn't find his own gas cap, he might be able to find one that fit.

Sure enough, after only a short time of searching, he found a gas cap. He carefully wiped it off and slipped it into place with a satisfying click.

"Great," he told his wife as he climbed back into the car, "I may have lost my gas cap, but I found another one that fits and it's even a better cap than the one I had - it locks..."