One day, John read an advertisement in a newspaper. It said "Wanted. The best salesman in the world." John thought he was a great salesman and went to ask for the job. "I'm the best salesman in the world," he said to the manager. "Give me the job."
"You must prove you're the best," the manager said.
"OK I will," John said.
"Good." The manager took several boxes of sweets out of his desk." Last week I bought a thousand boxes of sweets. If you can sell them all before the end of the week, you can have the job," said the manager.
"That's easy," John said. He took the boxes of sweets and left the office.
Every day and all day he went from shop to shop, trying to sell the sweets. But he couldn't sell one. The sweets were too bad for him to sell. At the end of the week he went back to the manager." I'm sorry, sir," he said," I was wrong about myself. I'm not the best salesman in the world, but I know who is."
"Oh" said the manager. "Who?"
"The person who sold you a thousand boxes of the sweets."