Difference between theoretical and realistic

A small boy has a school home work question to answer, so he asks his father " Hey Dad, what's the difference between 'theoretically' and 'realistically'?"

His Dad thinks for a while and then says "Righto son.....go and ask your mother if she'd sleep with David Beckham for a million quid."

The boy trots off and comes back saying "Dad, Dad, she said she would! She would sleep with David Beckham for a million pounds."

"OK, son," says his dad. "Now go and ask your sister the same question."

The boy toddles off, and comes back saying "Dad, Dad, she said she would, too!"

So, then his dad says "Right, son, now go and ask your elder brother if he'd sleep with David Beckham for a million pounds."

The son comes back excitedly saying "Dad! Dad! He said he would too!"

"Well, there you have it, son," said his dad. Theoretically, we could be sitting on three million quid. Realistically, we're living with two tarts and a poof."