There is a story about a man who takes the wrong road in the desert and has car problems.  He walks and finds an old deserted town with a water pump.  The pump isn't working.  As he was sitting there he saw a piece of paper in an old bucket which tells of a bottle of water hidden under a rock.  There is good water in the pump--but it needs to be primed with the bottle of water.  If the traveler drinks the water he won't have enough to prime the pump.  Which will he do?