After finishing an out-of-town errand, I discovered that my car wouldn't start because it was out of gas. A passerby told me there was a service station a half-mile away, so I took a gas can from the trunk and trudged the distance in the sweltering sun.
The attendant filled my two-gallon can, and I lugged it back and poured the gas into the tank. But when I tried to unlock the car door, it wouldn't open. Just then, I noticed an identical old car parked a short distance away. That was my car; I had filled a stranger's gas tank.
Wearily I walked back to the station. "You know," the attendant suggested helpfully, "instead of walking back and forth to fill the tank from the can, you could put a couple of gallons in the tank and then drive the car here."