Have you ever had the experience of having to drive a considerable distance to an appointment; but, the vehicle that you are driving shows that the gas gauge is closer to empty than you would like? You are in a hurry—late for your meeting—so you decide to see if you can make it. The red warning light comes on. Then the fuel gauge starts to rest solidly on the empty mark, and your stomach grows tighter mile by mile. Perhaps you make it—and perhaps you don't. And as the light stays on and the indicator sits on empty, you become more tense. When do you refuel?