For all the DD you do, there is no predicting the future.

Plus there is a very real incentive for companies to do shady things, e.g. Volkswagon or Enron.

Are you sure those companies you're holding aren't lying out of their ass? Can you prove that? Like, unless you're in the accounting dept. at those firms -- or someone who can otherwise get those numbers -- you can't.

At that point it's gambling. It may be akin to counting cards, where you can make probabilistic guesses, but best case is still uncertain.

Otherwise you're rocking a very special secret, or are manipulating the market. But for the rest of the us stock plebs, is effectively gambling.