Regardless of whether you trade with discretion or use a mechanical system, at some point you have to make decisions about when and why to get in and out of your positions. Although a discretionary trader may not know the precise answers to these questions until seconds before executing a trade, and a systematic trader might have effectively made these decisions weeks ago, both traders are presumably taking action for a reason.

The conclusions either trader makes are only as good as the data they are based on. It is unfortunate, then, that so many traders choose to either trade from the seat of their pants ("using their gut") or delve into complex system design without having any real understanding of how the markets they trade actually behave.

Different characteristics call for different strategies.