Market participants run the gamut from seasoned rational professionals to knee-jerk reactive amateurs. Professionals are the ones who are willing to take the other side during short term movements for long term profits. This softens the blow and improves markets for everybody. One thing that is left out of these discussions is that many of the market inefficiencies we're talking about are relatively uninformed orders trying to buy/sell at any price, which the professionals are racing against each other to trade with. In many cases, they're literally paying the brokerages for these orders. If modeling helped you be right 60% of the time, you would want to flip the coin as often possible.