Trading other people's money (usually a super-large amount of money), can be more profitable than trading your own money. A broker trading billions of dollars a year, can become much richer, than someone trading their own capital (usually a smaller amount of money).
A broker usually takes some form for commision, like 6 percent of profits. 6% of a whole lot of money can be much more than 100% of a traders own profits, if you understand what I mean.
