Oliver Renick and I had a good discussion about what caused (and didn’t cause) the equity market sell off in October 2018. I’m a market structure guy, not an equity strategist. But market structure certainly should be examined when thinking about why markets do what they do; in this case, the growth of passive investing and algorithmic trading. Ultimately our discussion came down to the role of high frequency trading in the sell off. Remember again that I’m not an equity strategist, but it doesn’t take an equity strategist to see that the market sold off because, well, investors began to sell. A feeling that things have been too good for too long has left many looking for the cause of the next crash, and that anxiety was and continues to be at play.