[abuckenheimer]

Yes HFT buys trade flow from robin hood because they make more money executing against it but that's not actually to the detriment of the people on the robin hood app. The main way HFT firms make money is by making a market, they offer to buy and sell stocks cheaper than anyone else and get paid by people crossing the spread and sometimes exchange fees. The reason robinhood trade flow is valuable to HFT firms Isn't because they are trading against "dumb" millennials but because they know millennials aren't likely to move the market playing around on their smartphone. HFT firms can collect a small rent sitting in between millenials trading with one another without the risk of being on the wrong side of a trade that materially moves the price of a stock.

Matt Levine does great write ups on this stuff, would highly recommend: https://www.bloomberg.com/opinion/articles/2018-10-16/carl-i...

[jcoffland]

The stock market is a zero sum game. If HFTs are making money then someone else's is losing it. The other traders who's trades are closest are the most likely losers. HFTs will tell you what a great liquidity service they provide but they are doing nothing more than using the equivalent of insider information to skim the cream off the top.

[tptacek]

This is a facile analysis. If you believe HFT internalizers are taking money from retail traders, try to outline the series of orders that results in money from the retail trader's pocket going into the HFT's pocket, and precisely how the retail trader could have made that same money on their own.

The reality is that market makers price non-retail flow more conservatively (ie: costing traders more) because they have to anticipate informed large block trades wiping them out. Since they don't have to do that for retail flow, their cost basis for those trades is lower, and they can (and do) split the proceeds of that reduced cost with brokerages.

It's overwhelmingly likely that any other brokerage you use does the same thing, and simply doesn't tell you or pass any of those savings on to you.

[gruez]

>The stock market is a zero sum game. If HFTs are making money then someone else's is losing it.

But who's that "someone else"? It's not the robinhood customer, because they're getting at least the best price on NMS[1]. So what's the issue? Would you rather pay $10/trade so your trade gets posted directly to the exchange and the profit goes to some random investment bank or daytrader rather than the HFT firm?

[1] https://en.wikipedia.org/wiki/Payment_for_order_flow#Legalit...

[snowwrestler]

The stock market is not a zero sum game. I don't know where people get this idea that because every transaction involves two sides, the sum is therefore zero. Every transaction in the "real economy" also has two sides, and we all know that grows. The stock market grows too. There are even indexes to track how well it is growing.

[barrkel]

Stocks are not zero sum. In theory, their value is based on future income. Information about the future is what most affects stock prices, because it changes expectations around future income. Even with no transactions in a stock, offer price can continue to rise because of these expectations, and it represents real increase in wealth to people who own the stock, no transactions necessary. When offer price rises enough to tempt someone to sell then you have an estimate of the market value.

[wglb]

But the zeroes that the HFTs are taking is from the old-line manual market makers, not sellers or buyers.

[im3w1l]

Here is my understanding. Let a<b<c be small numbers. Some investor thinks a stock is worth x+c. They put in a limit buy order at x. Some HFT firm sees this and thinks well if they want it at x, I want it at x, and puts in their own order at x (+a fees to robin hood). Millenial comes and wants to sell their stock.

Normally the investor would get the stock since they placed their order first. But since the HFT firm is paying for the order they get it instead. If things go well the HFT firm can sell to the investor at x+b, if things go poorly they cut their losses and sell at x.

The investor that didn't get the order and has to buy it from the HFT firm at x+b is the loser.

The money that funds this dance comes from the millennial who sold a stock worth x+c at x, but that would have happened regardless.