A man got a job as a night watchman at a factory. There had been a lot of thefts by the workers on the night shift, and so every morning when the night shift workers passed through his gate it was his job to check their bags and pockets to make sure that nothing was being stolen.
Things were going along very well the first night on the job until a man pushing a wheelbarrow of newspapers came through the gate. Aha, he thought, that man thinks he can cover up what he is stealing with that newspaper. So he removed the paper only to find nothing. Still he felt that the man was acting strangely, so he questioned him about the paper.
"I get a little extra money from newspapers I recycle, so I go into the lunchroom and pick up all the ones people have thrown away." The guard let him pass, but decided to keep a close eye on him. The next night it was the same, and the night after that. Week after week it went on. The same guy would push the wheelbarrow of newspapers past the guard's checkpoint. The guard would always check and find nothing.
Then one night, about a year later, the guard reported for work only to find a message had been left for him telling him to report to the supervisor. He walked into the supervisor's office and before he could say a word, the boss said, "You're fired!"
"Fired?" he asked in total surprise. "Why? What did I do?"
"It was your job to make sure that no one stole anything from this plant and you have failed. So you're fired."
"Wait a minute, what do you mean failed. Nobody ever stole anything from this place while I was on guard."
"Oh, really," the boss answered. "Then how do you account for the fact that there are 365 wheelbarrows missing?"