At school, a boy was told by a classmate that most adults are hiding at
least one dark secret, and that this makes it very easy to blackmail them by
saying, "I know the whole truth". The boy decides to go home and try it out.
He goes home, and as he is greeted by his mother he says, "I know the whole
truth." His mother quickly hands him a $50 note and says, "Just don't tell
your father.

"Quite pleased, the boy waits for his father to get home from work, and
greets him with, "I know the whole truth." The father also promptly hands
him a $50 note and says, "Please don't say a word to your mother."

Very pleased, the boy is on his way to school the next day, when he sees the
mailman at his front door. The boy greets him by saying, "I know the whole
truth." The mailman drops the mail, opens his arms, and says, "Then come
give your FATHER a big hug."