AN OLDER CARPENTER and his young, inexperienced apprentice were building a small barn. As they were preparing to attach the siding, the chief carpenter showed the young fellow how to hold the boards while nailing them to the studs, then left him on his own.
After a short while, the chief returned to check up on the lad. He noticed that the youngster was throwing about half the nails he pulled from his apron onto the ground. "Why are you throwing away so many nails?" asked the carpenter. "Well," the young man explained, "sometimes I can't hammer in a nail because when I pull it out of my apron, the head is on the wrong end. So I discard it."
"You knucklehead!" shouted the chief. "Don't throw away the nails with heads on the wrong ends--they're for the other side of the barn!"