An economist had finished his day at work and was leaving for home, when he noticed a small boy call out to him from the footpath where he was sitting with a dog. The boy said, "Sir, would you like to buy a dog." The economist was surprised by the approach, but asked nevertheless, "How much are you selling the dog for?" The boy replied "Twenty thousand dollars." "Twenty thousand dollars for this dog!" the economist exclaimed. "Does he know any special tricks to make him worth so much money?" The boy replied, "Sir, this dog never made a dime in his life. If you take into consideration the expenses on his food, I think you will lose money on him every year." The economist did not want to let go the opportunity to lecture the boy about the principles of economics and explained to him the fact that a commodity needed to yield more returns than it consumed to equal a purchase price. He finished by