The history of the past fifty years, and longer, indicates that a diversified holding of representative common stocks will prove more profitable over a stretch of years than a bond portfolio, with one important provisio—that the shares must be purchased at reasonable market levels, that is, levels that are reasonable in the light of fairly well-defined standards derived from past experience.

Chapter I, What the Intelligent Investor Can Accomplish, p. 7 - The Intelligent Investor: The Classic Text on Value Investing (1949)