Wednesday, December 7, 2016

Matt Levine is hilarious

That's about the October 7 "flash crash" of the pound in thin overnight trading. There's a common explanation of flash crashes in which a falling price triggers a bunch of stop orders, forcing automatic selling at a time when there aren't any buyers, pushing the price down further and triggering another wave of stops. In this story, the stop order -- an automatic order to sell if the price gets too low, meant to limit an investor's risk in a falling market -- is the culprit. It's a sort of crystallized form of pre-panic: The investor surveys the possible future states of the world, decides that if the pound falls below $1.25 she'll panic, and gives her broker instructions to panic for her if she's not around to do it herself.But the stop order is just a tool to implement the panic. You don't need the stop orders to have the panic. You can just be there, and panic. (Or: You can not be there, because it's the middle of the night, and your less experienced trader in Tokyo can panic for you.) The reason stop orders exist is because they correspond to a popular human behavior: When the price of your position falls, you want to get out of it, so you sell as quickly as you can. This is not always a smart behavior -- sometimes it is! -- but it is common enough that an order type exists to automate it. But you can have the behavior without the order type. That seems to be what happened here.
We need a new term, Bot Hysteria, bot pre-programmed to panic at certain conditions.  It is a necessity, our desire to panic now and then is overwhelming.

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