An adequate theory of depressions, then, must account for the tendency of the economy to move through successive booms and busts, showing no sign of settling into any sort of smoothly moving, or quietly progressive, approximation of an equilibrium situation. In particular, a theory of depression must account for the mammoth cluster of errors which appears swiftly and suddenly at a moment of economic crisis, and lingers through the depression period until recovery. And there is a third universal fact that a theory of the cycle must account for. Invariably, the booms and busts are much more intense and severe in the “capital goods industries” — the industries making machines and equipment, the ones producing industrial raw materials or constructing industrial plants — than in the industries making consumers’ goods. Here is another fact of business cycle life that must be explained — and obviously can’t be explained by such theories of depression as the popular underconsumption doctrine: that consumers aren’t spending enough on consumer goods. For if insufficient spending is the culprit, then how is it that retail sales are the last and the least to fall in any depression, and that depression really hits such industries as machine tools, capital equipment, construction, and raw materials? Conversely, it is these industries that really take off in the inflationary boom phases of the business cycle, and not those businesses serving the consumer. An adequate theory of the business cycle, then, must also explain the far greater intensity of booms and busts in the non-consumer goods, or “producers’ goods,” industries.