This article is general information, not a recommendation to buy or sell anything. Academy articles are prepared by the ETTFOS team and other writers. They make no claim of expertise or accuracy, and they are not kept up to date after they are published.
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Every trade involves the same decisions: what to buy or sell, when, how much, and when to get out. The only question is when they are made.
A written system makes them before the trade, while thinking is calm. Without one, they are made during the trade, while money is moving.
What a trading system is
A trading system is a set of written rules that turns a view of the market into actions. It says which markets to trade, what must happen before a position is opened, how large the position may be, and what ends it.
The test is simple: two people following the same rules should make the same decisions. If a rule needs a feeling to apply it, it is not yet a rule.
Why decisions made in the moment go wrong
Without written rules, the decision is borrowed from somewhere else. The SEC warns day traders to watch out for “hot tips” and “expert advice” from newsletters and websites, and adds: “Don’t believe claims of easy profits.” In its research on newer investors, the UK’s Financial Conduct Authority (FCA) found they were “more reliant on contemporary media (e.g. YouTube, social media) for tips and news.”
Signals and bots promise to take the decision away altogether. The CFTC warns that fraudsters tout “automated trading algorithms, trade signal strategies, and crypto-asset trading schemes” that promise unreasonably high returns. Its plain answer: “AI technology can’t predict the future or sudden market changes.”
A tip, a signal and a bot have one thing in common: the person acting on them cannot see the rules behind them. With a written system, every rule is known, and so is every reason.
What a written system covers
- Markets and time frame: which markets the system trades, and over what holding period.
- Entry: the conditions that must all be true before a position is opened.
- Exit: where the trade is wrong and closes at a loss, and where it has done its job.
- Size: how much of the account a single position may put at risk.
- Limits: the most the account may lose in a day or a week before trading stops.
- Records: what is written down about every trade, so the rules can be checked.
None of this needs to be complicated. All of it needs to be written down before it is needed.
Testing a system honestly
Rules can be tested on past prices before real money follows them, and the limits of that test are worth knowing. Under US futures rules, simulated results shown by trading advisors and pool operators must carry a warning such as this: the results “do not represent actual trading”, and simulated programs are “designed with the benefit of hindsight.”
A back-test also leaves out what trading feels like: a simulated loss is easier to sit through than a real one.
Past results are not indicative of future results.
A tested system is not a promise of profit. It is a set of rules whose behavior is known, including how it loses.
Stops are rules, not shields
A losing trade is often closed with a stop order, which the CFTC defines as “an order that becomes a market order when a particular price level is reached.” Once it is a market order, it fills at the price available, which in a fast market can be well away from the stop.
That is why size belongs in the system too. The stop decides where a trade ends; the size decides what that ending costs.
The takeaway
A written system does not make markets predictable. It makes the trader predictable, which is the part a trader can control. The decisions are made once, calmly, and then followed.
That is the value of a written system: when the pressure arrives, the thinking has already been done.
Your results will depend on your own decisions, your capital and market conditions, and you can lose money.
