>What does this even mean? "Eventually the pool runs out of water". What?
Well, when you have a pool, and water is constantly being sucked out of it, even a tiny bit at a time, eventually you will have no water left in the pool. Not a hard concept.
Well, let me say it's not backwards, it is just nonsensical. Market making HFTs don't have any built in mathematical edge like a roulette wheel. Further, they lower the cost of trading, they add money into the pool in the form of the risks they take and the infrastructure they create.
As I look around the markets, I don't see a lot of participants that are there to lose money. The ability to make a profit from market activities is central to a correctly working market.
Well, when you have a pool, and water is constantly being sucked out of it, even a tiny bit at a time, eventually you will have no water left in the pool. Not a hard concept.