1984

Buffett argued that the efficient-market hypothesis could not account for a cohort of investors who, sharing a common intellectual origin in Ben Graham's teachings, had independently produced long-term records of outperformance. He used a coin-flip analogy: if a national coin-flipping contest produced a handful of winners after many rounds, one would ask whether the winners shared a common method, not whether they had each been lucky.

On the common method shared by the value-investing cohort.

Buffett emphasized that the investors he cited were not making the same investments; they owned different businesses, in different industries, with different concentrations. What they shared was a disposition: the willingness to act only when price offered a genuine margin of safety relative to value, and the temperament to do nothing when no such opportunity existed. He argued that temperament, rather than intellect, was the differentiating factor the hypothesis could not model.

On temperament as the true common factor.