"An 'efficient' market is defined as a market where there are large numbers of rational, profit-maximizers actively competing, with each trying to predict future market values of individual securities, and where important current information is almost freely available to all participants. In an efficient market, competition among the many intelligent participants leads to a situation where, at any point in time, actual prices of individual securities already reflect the effects of information based both on events that have already occurred and on events which, as of now, the market expects to take place in the future. In other words, in an efficient market at any point in time the actual price of a security will be a good estimate of its intrinsic value." - Fama, 1965 It is poor and misleading for the speculator. Not all participants receive the information at the same time, and all are subject to interpret that information differently. In fact, these is no such thing as "intrinsic value". The idea is that there is some fair value for a stock, and the best estimator of that value willl win, by identifying when this value does not correspond with current prices in the marketplace. In fact, the "fair value" does not exist and the stock is worth exactly what someone is willing to pay for it at that moment in time.