Suppose you were asked to walk along a narrow plank that was resting on the floor. You would do it easily, without question. But now suppose the same plank were twenty feet up, stretching between two walls. Would you walk it? Could you? Probably not. Your desire to walk the length of the plank would come into conflict with your imagination. You would imagine yourself toppling off the plank and falling a long way to the ground. You might very much want to walk across the plank, but your fear of falling would keep you from being able to do it. The more effort you put into
