But with too little air, it falls to the floor. Greenspan helps decide when to blow more air into the economy. In this case, the air in a balloon is the amount of money in the economy. Greenspan can make the economy grow by increasing the money supply, or keep the economy from inflating too much by decreasing the money supply. His goal is for the economy to grow and contract gradually.
Rapid changes can harm businesses and consumers.
Another way of thinking about it is like starting a car. If you floor the gas all of a sudden, your passengers get jolted back into their seats. If you slam on the brakes, they hit the windshield, or at least get a bad case of whiplash. The idea is to slowly change the pace of economic growth, so no one gets hurt. And since Greenspan has his foot on the gas pedal, his every move is watched by investors around the world.