> What if it takes 12 months of hard thinking to draw the right conclusion from the information? Are there many investors who go to such lengths?

It's not required to be all of them. Suppose that it indeed isn't, but the ones who do that work for investment funds who control significant pools of money.

Now the investors in two or three of those places do the research and conclude that some company is about to start doing well and their share price is currently $50 but is about to be $150. So they start buying it, and keep buying it until it gets up near $150. Which happens pretty quickly because they control enough money to use up all of the short-term liquidity at the lower prices and the majority of the shares are held by people who aren't even paying attention and therefore don't try to sell when the price starts going up. Once the price gets to that point they don't buy any more because it's no longer selling at a discount.

Then the company actually starts doing well to the point that everyone can see it but the price hardly moves because it was already priced in.