Successful traders have one common trait. They follow a set of pre-defined rules. When this happens, buy that. When that happens sell this. Whether they are programmed into a language that a computer can read or in the mind of the person trading, the rules exist.
It's that simple. To be a successful trader you need to have rules and you need to honor those rules. Otherwise the following happens, something we have all experienced first hand.
The revenge trade, I'm so mad I just lost, I'm going to trade and get that money back.
I'm going to move that stop, I think the market is going to rally soon.
But earnings were so good, I can't sell now.
I want to take this trade, but I'm afraid even though my rules have been met.
A system can essentially eliminate these type of traps. The emotional bias that all traders bring to the market each day is removed when trading with a system. Decisions like should I keep trading even though I just lost or have a few wins is not answered in the noise of battle, but in the solitude of system design.
So whether you are a long term investor who writes call options or a full-time intraday trader, systematic trading is the ideal solution for many.
Bottom line. Every successful trader has pre-determined rules they strictly follow. And any rule can be programmed. So rather than ask "why trade a system" one should ask "why not."
When you consider how the barrier to entry has been reduced,
what is stopping you from trading systematically?