Comment by ctkrohn

Right, those anomalies could simply exist unexploited until the market is better understood. For example, you used to be able to earn money buy buying the 501st largest company in the US: if it happened to become the 500th largest, all the S&P 500 index funds would be forced to buy its stock, and it would outperform the other stocks that had already been in the index. Similarly, the 500th largest stock would be a good sale candidate: if it becomes the 501st largest company, the index funds will become forced sellers. Now this effect is very well known, and there's no more money to be made by exploiting it.