A kid comes home from school with a writing assignment. He asks his father for help. "Dad, can you tell me the difference between potential and reality?"
His father looks up, thoughtfully, and then says, "I'll demonstrate. Go ask your mother if she would sleep with Robert Redford for a million pounds.
Then go ask your sister if she would sleep with Brad Pitt for a million pounds. Then come back and tell me what you've learned."
The kid is puzzled, but decides to ask his mother. "Mum, if someone gave you a million pounds, would you sleep with Robert Redford?"
"Don't tell your father, but yes, I would," she replies. He then goes to his sister's room. "Sis, if someone gave you a million pounds, would you sleep with Brad Pitt?"
She replies, "Omigod! Definitely!"
The kid goes back to his father. "Dad, I think I've figured it out. Potentially, we are sitting on two million quid, but in reality, we are living with two sluts."