The Brains Trust, page-8211

There was a video I saw a while ago which had an interview with one of the (i think) Goldman S. ex-traders. He was talking about how those companies make money off people. There were a few different streams, but there are three streams relevant to this discussion.

One was the obvious (brokerage). Another one was that these firms actually analyse your trades and your account. If you are a successful trader, they will also open positions to mirror yours (and perhaps take the stock on market before you have a chance to buy it...). Conversely, if you have a bad trading record they'll go short when you go long and vica versa.

It's all very interesting