The central thesis of A Random Walk Down Wall Street is the Random Walk Hypothesis. Malkiel argues that the short-term movements of stock prices are largely random and unpredictable, much like the path of a person walking randomly. Because of this randomness and the general efficiency of the market (meaning prices quickly reflect all available information), it is extremely difficult, if not impossible, for most investors (including professional fund managers) to consistently outperform the overall market averages through stock picking or market timing.