What efficient markets says is that prices today contain the available information about the future. Why? Because there’s competition. If you think it’s going to go up tomorrow, you can put your money where your mouth is, and your doing it sends (the price) up today. Efficient markets are not clairvoyant markets. People say, “nobody foresaw saw the market crash.” Well, that’s exactly what an efficient market is—it’s one in which nobody can tell you where it’s going to go. Efficient markets doesn’t say markets will never crash. It certainly doesn’t say markets are clairvoyant. It just says that, at that moment, there are just as many people saying its undervalued as overvalued.
To be filed under “not understanding the difference between necessary and sufficient conditions”.