We can reasonably hypothesize that “Mr. Market” is rational, and knows a lot of stuff, because there are a lot of people out there looking to make a buck off of any slip-up, looking to get an edge, to learn something he doesn’t know, and to trade on that basis. Further, all their trades on the basis of what they learn in that effort make him smarter. They contribute to determining prices, so that an “edge” that still worked a month ago may be outdated now, as Mr. Market has learned to factor it in. And that is why (especially according to advocates of the ECMH) stock prices move in a random walk. It is random to any observer not as smart as Mr. Market himself. Any given neuron will presumably see the thoughts of the whole of the brain as a random result of who-knows-what. There is nothing mystical about this – the confused neuron, in its own trading, helps to bring the situation about. Now, when I’m asked whether I believe in ECMH, I generally reply, “yes and no.” It ...