Meaning of... 'potentially' and 'realistically'

A young boy went up to his father and asked him, "Dad, what is the difference between 'potentially' and 'realistically'?" The father thought for a moment, then answered, "Go ask your mother if she would sleep with Brad Pitt for a million dollars. Then ask your sister if she would sleep with Brad Pitt for a million dollars, and then, ask your brother if he'd sleep with Brad Pitt for a million dollars. Come back and tell me what you learn from that." So the boy went to his mother and asked, "Would you sleep with Brad Pitt for a million dollars?" The mother replied, "Of course, I would! We could really use that money to fix up the house and send you kids to a great university!" The boy then went to his sister and asked, "Would you sleep with Brad Pitt for a million dollars?" The girl replied, "Oh, good heavens! I LOVE Brad Pitt and I would sleep with him in a heartbeat. Are you nuts?" The boy then went to his brother and asked, "Would you sleep with Brad Pitt for a million dollars?" "Of course," the brother replied. "Do you know how much a million bucks would buy?" The boy pondered the answers for a few days and then went back to his dad. His father asked him, "Did you find out the difference between 'potentially' and 'realistically'?" The boy replied, "Yes, 'Potentially', you and I are sitting on three million dollars, but 'realistically', we're living with two hookers and a future congressman."