[tptacek]

HFTs don't corner the market for a particular instrument. So what's really happening is more like the market for limited- release sneakers. They rush to the store, they buy up a bunch of sneakers. Now they're holding inventory. They only make money if they can sell that inventory off for more than they paid for it.

But there are thousands of other places where the same shoes are being sold. If the demand for the particular sneakers they bought climbs, they will make money. But it's just as likely that the demand will fall (in fact, it's much more likely that demand will fall in the instruments HFTs trade --- that's what those instruments do! They take random walks!), in which case that inventory they bought is a liability.