I often see the mentioned that only 1% of forex traders manage to make profits for a long period of time. What this shows is the fact that while it IS possible, it isn't as easy as a lot of people would have you believe. Only the best of the best earn enough to live off and it takes years to get to that point
And these 1% might well be banks
Banks will make profits at Forex no matter where the price might move since when they either buy or sell they are already fixing profits that they earned on their clients before. This is essentially the same with other markets too. Not all markets are a zero-sum game, but if they are, that basically means that those who are making profits (the said 1% of profit takers) are leaving the rest of the trading folk with losses. It is hard to beat the banks but still not impossible. George Soros did exactly that, i.e. made the Bank of England bite the dust in the early 1990s