"The gravitation constant is the same always. But the economic constants-these elasticities of demand and supply-depending, as they do, upon human consciousness, are liable to vary. Prosperity ends in a crisis. The era of optimism dies in the crisis, but in dying it gives birth to an era of pessimism. This new era is born, not an infant, but a giant; for an industrial boom has necessarily been a period of strong emotional excitement, and an excited man passes from one form of excitement to another more rapidly than he passes to quiescence. Under the new error, business is unduly depressed."

Source : "The Economics of Welfare". Book by Arthur Cecil Pigou (4th edition, 1932), Ch. 1 : Welfare and Economic Welfare, § 4, 1920.

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