An Open Door
Think of the gambler who is in the midst of a long dry spell in Las Vegas.
Eventually he gambles away all his money and has to borrow a quarter from another gambler just to use the men's room. He finds a stall that happens to be open and pockets the quarter.
When he goes back onto the floor, he puts the quarter in a slot machine and hits the jackpot. He takes his winnings and goes to the blackjack table and turns that money into $1 million.
Wealthy beyond his wildest dreams, the man goes on the lecture circuit, where he tells his incredible story. He tells his audiences that he will always be eternally grateful to his benefactor, and if he ever finds the man he will share his fortune with him.
After months of speaking, a man in one audience jumps up and says, "I'm that man. I was the one who gave you the quarter."
"Yes, I remember you well, but you aren't the one I'm looking for," the speaker says. "I mean the guy who left the door open!"