From Security Analysis, 1940 edition:
"Characteristically, stocks thought to have good prospects sell at relatively high prices. How can the investor tell whether or not the price is too high? We think that there is no good answer to this question —in fact we are inclined to think that even if one knew for a certainty just what a company is fated to earn over a long period of years, it would still be impossible to tell what is a fair price to pay for it today.....On the other hand, assume that the investor strives to avoid paying a high premium for future prospects by choosing companies about which he is personally optimistic, although they are not favorites of the stock market. No doubt this is the type of judgment that, if sound, will prove most remunerative. But, by the very nature of the case, it must represent the activity of strong-minded and daring individuals rather than investment in accordance with accepted rules and standards."