The investor has a right to expect good results to flow from a consistent and courageous application of the principle of buying after the market has declined substantially and selling after it has had a spectacular rise. But he cannot expect to reduce this principle to a simple and foolproof formula, with profits guaranteed and no anxious periods.

Chapter II, The Investor and Stock-Market Fluctuations, p. 33 - The Intelligent Investor: The Classic Text on Value Investing (1949)