A son asked his father, "Dad, what's the difference between theory and reality?"  
The father handed his son a Vintage Car magazine and said, "son, look up the value of a '68 Chevrolet pick-up and a '69 fastback Mustang.  
The son did as requested and came back shortly with the answers: "$19,500 for the truck and $35,000 for the Mustang." 
Then the father said, "now go over next door and ask uncle George how much he'll give you for those two vehicles parked behind the shed."  
The son does as his father asks and returns shortly with a less than enthusiastic answer, "$100 each Dad."  
The father says, "there you have it son."  
Puzzled, the son replies, "there you have what, dad?"  
The father says, "well, in theory son, we have $54,500 worth of automobiles in the back yard, but in reality we own a $200 pile of scrap metal!"