Society has advanced from a state of general poverty to widespread prosperity through the use of machinery and labor-saving devices, increasing productivity by allowing a higher degree of specialization and division of labor. All that machines really do is harness the laws of nature for the satisfaction of human needs and wants. Politicians and economists use the metaphor of the machine as a model for the economy and society. They presume that, like a machine, the economic engine responds predictably to their manipulations. The machine metaphor breaks down, however, when one realizes that, rather than having levers and buttons on a control panel, an economy has millions of simultaneous, independent, uncontrollable and unpredictable inputs.