Quote from dont:
Its random or very near to. But not efficient. Think about it if it was efficient there would be no trade Volatility would be close to zero.
I'm not sure if you're aware but volatility is actually proves efficiency. An inefficient market such as communism will have set prices that are either cheap or expensive to the curve. A volatile market shows continuous price discovery. Just because prices are swinging this way and that doesn't necessarily mean we aren't in equilibrium, there is a buyer for every seller, so price discovery has matched supply and demand at that point in time.
Now, points towards market inefficnecy. Well, the most important one is gaps in hte market, caused by our 9:30 to 400 market. Another would be if Wall street insiders knew about public info before others, and were able to trade on that. There are others, but I think some people mis-interpret what efficiency really is, and it doesn't mean that markets are untradable if they are efficient, just that you have no more advantage than the guy sitting next to you.