Comment by shmee on The EMH Aten't Dead · 2020-07-31T20:08:16.306Z · LW · GW

I lost the thread when I got to the section "If You're so Smart, Why Aren't You Rich?". An assumption seems to become implicit there that if the EMH is false, then you can beat the market. But why is that so? I tend to think of the market as a random walk during day trading, largely driven by viral memetic fashion trends on the scale of weeks to months, and then often only "weighing" effectively on the scale of months to years.

Take the day trading example: the S&P had almost no cumulative returns during the day from 1993-2017, while after-hours & pre-market were ~600%. If market moves during the day are a random walk, then clearly they are not efficient *and* one cannot beat the market consistently, over that short time window.

Over the last couple of years of trading options, my least favorite source of randomness has been Trump tweets. I think it would be very hard to argue that the market prices them efficiently or that it is possible to have an edge in predicting them but they sure do move prices around and destroy your trading positions.