From another site

So little johnny comes home from school and asks his dad whats the difference between potentially and realistically. He tells his son to go ask his mother and sister if they would sleep with any man for 1 million dollars, Johnny runs off and returns a few mintues later. Tells his dad that both said they would. Johnnys dad says "See son, potentially we're sitting on 2 million dollars but realistically we're living with 2 s."