 Milton Friedman believed that this was a key contributor to the Great Depression of the 1930s.John Maynard Keynes believed, and subsequent Keynesians believe, that unstable aggregate demand leads to macroeconomic instability, while real business cycle theorists believe that fluctuations in aggregate supply drive business cycles.Economic instability can have a number of negative effects on the overall welfare of people and nations by creating an environment in which economic assets lose value and investment is hindered or stopped.