A young boy was told by one of his friends that most adults are hiding at least one dark secret, and that this makes it very easy to blackmail them simply by saying: "I know the whole truth." The boy decided to go home and put the theory into practice. Greeted by his mother, he announced: "I know the whole truth." She quickly handed him $20 and said: "Please don't tell your father." Delighted with the result, the boy waited for his father to arrive home from work. Then he greeted him with: "I kn…