Great question Herman! The trick is knowing what the probabilities are of your trade/setup working. This of course requires a fair amount of homework. You need to know from a statistical basis, things like how far the market is likely to go, whats its' minimum movement, what is the average drawdown, what is the volatility, what is a typical daily trading range etc.. In other words, know your market inside out! Once armed with that sort of knowledge, you hunt down a repeatable pattern and trade it. If it brings home the bacon 90% of the time, you're in business. If you trade without knowledge of the aforementioned "stuff", then you're gambling. Know your market inside and out!
Rob