There is certainly plenty of debate about just how random the market is. Whether it is random and unbiased or slightly randomised around a genuine structure is the key to determining whether or not trading systems can actually work.

First of all, if markets are in fact genuinely random in the truest sense of the word, then a money management system based on limiting the size of all trades so that luck will eventually bring profit won't really work. By setting a profit target and a loss limit, merely making the loss stop a tight one will not actually benefit the trader in any way. In a random market, a loss stop three times closer than a profit target will be hit three times as often. You don't gain an edge, in fact you may lose it because of your commissions.

In my own experimentations, I spent several days "trading" coin flips and dice throws. The above idea, which comes from W Gallagher's Winner Take All, seems to bear this out. I had plenty of "trends" establish themselves and I dutifully rode those as high as I could with a variety of different chasing stops set up once the trend went outside of the profit target zone, but while the profits from a few lucky trades were indeed excellent, I hit my loss stop approximately three times as often as I hit my profit stop when I had a risk:reward ratio of three, four times as often when my ratio was four.

This is probably one reason why so many professional traders recommend you get out of the market when it seems to be just rolling around in a random fashion, it is untradeable because all it does is churn your account and generate lots of commissions for your broker, ensuring a similarly consistent stream of losses.

If we consider the alternative, that the market does have trends and structure, then there must be some sort of bias in the results, one direction of the market must be more favourable and traders can profit with a system to catch some sort of trend, or profit from more sudden moves when executed in a contrarian manner.

It is a tired old cleche that traders make their money in trending markets. You need something definitely non-random about the movements of the market, ie a trend that is driven by something other than luck. If the market does trend, you will either be stopped out or make decent money. Provided that you stay in the game long enough (and the purpose of money management is to keep you in as long as possible), eventually you will get a trend right and provided that you exploit it as well as you can you will make a profit.