A man recently volunteered to perform a parachute jump for charity. The first day of training, the instructor made an important point about preparing for landing at 300 feet.
"How do you know when you're at 300 feet?" asked one new jumper.
"A good question," replied the instructor. "At 300 feet you can recognize the faces of people on the ground."
The jumper thought about this for a while before saying, "What happens if there's no one there I know?"