John left the United States in 1969 to work in Africa. Africa was hot, and when John came back to the United States in 1979, he said to himself, "It's much colder here than it was before I left. I'm going to buy an electric heater. Also, everything is much more expensive."
John went to a store the next day to buy an electric heater. The salesman showed him three or four different kinds and then said, "And this is our best electric heater. It costs a lot of money, but it saves half of your electricity, and electricity is very expensive now, isn't it?"
"Yes, it's very expensive," John answered," and it's becoming worse every year." He looked at the electric heater carefully, thought for a few seconds and then said, "Well, I'll take two of these, please, and then I'll save all of my electricity."