A boy comes home from school one day and says to his father " Dad I need to explain to my class the difference between plausable and probable but I am having trouble telling the difference" Dad tells the boy " I can help you with that. Heres what you need to do. Ask your mother, your sister and your bother the following question then come to me with their answers. Would you sleep with a man for a million dollars. " The boy looks at his dad, says ok and goes off to ask his family the question. His Mom says yes of course, his sister answers the same and his brother does as well. He goes back to his dad and tells him " They all said yes, but I dont understand how this helps me." Easy says his dad. "With those answers it is plausable that we are sitting on three million dollars but its probable that we're living with two whores and a queer".

I love this joke. I've also heard it as potential vs. reality.