Well, then if it means that "buying a stock will always be a crapshoot, but we still can accumulate the best data possible to eliminate the really bad decisions.
For example, investing in 100 shares of GE might be a really bad decision. But the odds say that I would be quite likely to enjoy a decent return if I hold this stock long enough. If I compare this to buying the same dollar amount in Powerball tickets, the GE decision is certainly the wisest. It is POSSIBLE that it is not the best decision, but in investing LIKELY trumps POSSIBLY.