Benjamin Graham was a British-born American economist and professional investor. Graham is considered the first proponent of value investing, an investment approach he began teaching at Columbia Business School in 1928 and subsequently refined with David Dodd through various editions of their famous book Security Analysis. Graham's followers include Warren Buffett, William J. Ruane, Irving Kahn, Walter J. Schloss and others. Buffett, who credits Graham as grounding him with a sound intellectual investment framework, described him as the second most influential person in his life after his own father. In fact, Graham had such an overwhelming influence on his students that two of them, Buffett and Kahn, named their sons, Howard Graham Buffett and Thomas Graham Kahn, after him.
The individual investor should act consistently as an investor and not as a speculator. This means... that he should be able to justify every purchase he makes and each price he pays by impersonal, objective reasoning that satisfies him that he is getting more than his money's worth for his purchase.
Most of the time common stocks are subject to irrational and excessive price fluctuations in both directions as the consequence of the ingrained tendency of most people to speculate or gamble... to give way to hope, fear and greed.