Stanley 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, he hadn't been searching long when he found a gas cap.
He tried it on, and it went into place with a satisfying click.

"Great," Stanley thought, "I lost my gas cap, but I found another one
that fits. And this one's even better because it locks...