In one sentence
An order that automatically sells an asset once its price falls to the level you set.
A stop loss is an order that automatically sells an asset once its price falls to the level you set. It turns your maximum acceptable loss into a rule that executes on its own, without you staring at the screen.
It’s the tool that separates trading with a method from trading on hope. Before opening a position, you decide how much you’re willing to lose if the market goes against you; the stop loss signs that contract for you. In a market that trades 24/7 and can drop 15% while you sleep, having that order in place is the difference between managing risk and collecting surprises.
How a stop loss works and its two variants
You set a trigger price below the current price. If the market touches it, the order fires. In the market variant, it sells immediately at the best available price: it guarantees the exit, not the price (in violent drops it can execute below the level, the famous slippage). In the limit variant, you also set a minimum acceptable price: it guarantees the price, not the exit (if the market crashes and blows through your limit, you can be left inside watching the fall). Choosing between the two is choosing which risk you’d rather take.
There’s a third variant worth knowing: the trailing stop, which automatically rises behind the price at a fixed distance. If you buy at 100 with a 10% trailing stop and the asset rises to 150, your stop is no longer at 90: it moved up to 135. It protects gains without you having to move anything.
Where to place the stop loss, the art behind the technique
The beginner’s mistake is placing it too close “to lose little”: normal market noise sweeps it away, the position closes, and the asset keeps going without you. The stop needs room to breathe. There are useful references, like below a relevant support level (if the support breaks, your thesis was wrong and exiting is correct), or at a distance calibrated to the asset’s volatility (the ATR helps you size how much it “normally” moves).
The other half of the calculation is position size. The classic rule says not to risk more than 1-2% of your total capital on a single trade. If your stop is 10% below your entry price and you want to risk a maximum of 1% of your account, the position should be 10% of your capital. Risk gets defined first; the size of the purchase is a consequence, not a whim.
A stop loss with numbers
You buy ETH at $2,000. You place the stop loss at $1,800 (10% down, below the last support) and a take profit at $2,600 (30% up). Your risk/reward ratio is 1:3: you risk $200 to make $600. If ETH falls, you lose $200 per unit and that’s it: no drama, no averaging down, no “hang on a little longer.” If it rises, the gain pays for three losing trades like this one. At 1:3, you can be right once out of every three times and still stay in the green.
The classic stop loss mistakes (all avoidable)
Moving it down as the price approaches (“it’s bound to bounce”): at that moment you canceled your risk management. Trading without a stop “because it’s a long-term investment”: if it was long-term, why are you checking the price every hour? Placing it at exact round numbers where everyone’s stops pile up (sharp moves tend to sweep those levels before reversing). And the most expensive one of all is not placing it, which is statistically the fast track to turning a 10% loss into a 40% one.
Mental stop versus real stop
There’s the artisanal variant, the “mental stop,” the promise that you’ll sell yourself once the price hits a certain level. In theory it works the same; in practice it’s where trading plans go to die. When the price touches your level, the mind renegotiates (“I’ll wait for the bounce,” “it’s oversold,” “it’s manipulation”), and a market open 24/7 guarantees the decision catches you tired or asleep. The real order exists precisely to take execution away from the same mind that already proved, by buying at the top at least once, that it negotiates poorly under pressure.
