To do that you need to find stocks that are incorrectly priced, ones that the market undervalues. Countless investors and money managers claim the ability to do just that. An important dimension of the stock market is how it operates as an information processor. Each stock's price is the focal point of enormous amounts of information. Like a moveable fulcrum on a teeter-totter, the stock's price balances all the good and bad news about the company.
Flexible prices play a crucial role in making the stock market efficient.
Stock prices change frequently and in small increments, instantaneously adjusting to and incorporating any new information. Virtually all the theory and evidence points in the same direction. In contrast, most everyone in the Wall Street community denies that the EMH is true. That's not too surprising given the fact that hundreds of thousands of jobs are devoted to the purpose of trying to beat the market. Acceptance of the EMH would make most of those jobs redundant.