The basic belief of supply-siders is that supply creates demand, and what is supplied, will be consumed. To raise the level and quality of consumption one must raise supply. Supply-siders use the works of John Maynard Keynes to support their theory. Keynes can be seen as reinforcing supply-side notions of economic behavior. Keynes saw the individual capitalist at the center of the capitalist economy, and he regarded that capitalist's state of confidence as the most important source of economic development or decline.
Businessmen have to be confident in the future to be tempted to risk their capital.
While Keynes advocated enormous government expenditures to restore the confidence in businessmen and entrepreneurs during the Great Depression, the supply-siders, advocate that government play a different role. The best way for government to restore confidence is to cut taxes and cut back government intervention in the private sector of the economy. What the supply-siders want is an economy where the businessman feels free to exercise his powers and confident enough of the rewards he will receive for his own labor that he will work and invest. The supply-side doctrine fits very closely to Reagan's own vision of a capitalist system restored to the level of functioning it once enjoyed. Supply-side ideas like the Laffer curve became a central part of his economic program.