Yet simple fluctuations and changes do not suffice to explain that
  terrible phenomenon so marked in the last century and a half--the
  'business cycle.' The business cycle has had certain definite features
  which reveal themselves time and again. First, there is a boom period,
  when prices and productive activity expand. There is a greater boom in
  the heavy capital-goods and higher-order industries—-such as industrial
  raw materials, machine goods, and construction, and in the markets for
  titles to these goods, such as the stock market and real estate. Then,
  suddenly, without warning, there is a 'crash.' A financial panic with
  runs on banks ensues, prices fall very sharply, and there is a sudden
  piling up of unsold inventory, and particularly a revelation of great
  excess capacity in the higher-order capital-goods industries. A painful
  period of liquidation and bankruptcy follows, accompanied by heavy
  unemployment, until recovery to normal conditions gradually takes place.
                               -- Murray Rothbard, 1962