The difference between 'potentially' and 'realistically'

A son asked his father what's the difference between 'potentially' and 'realistically'?"

The father pondered for a while, then answered, "Go and ask your mother if she would sleep with Robert Redford for a million pounds. Also, ask your sister if she would sleep with Brad Pitt for a million pounds.

Come back and tell me what you have learned."

So the boy went to his mother and asked, "Would you sleep with Robert Redford for a million pounds?"
The mother replied, "Of course I would. I wouldn't pass up an opportunity like that"

The boy then went to his sister and said, "Would you sleep with Brad Pitt for a million pounds?"
The girl replied, "Oh gosh!! I would just love to do that! I would be nuts to pass up that opportunity!!"

The boy then thought about it for two or three days and went back to his dad.
His father asked him, "Did you find out the difference between 'potentially' and 'realistically'?"

The boy replied, "Yes, potentially we're sitting on two million pounds, but realistically we're living with two slappers."

The father replied, "That's my boy!"