Picture a roulette wheel that has landed on red eight times in a row. Many people feel black must be due. It is not. The wheel has no memory, and the chance of black on the next spin is exactly the same as it was on the first. That instinct, the belief that past random outcomes change the odds of the next one, is the gambler’s fallacy. It is surprisingly common in trading, where it can push people into decisions that feel logical but are not.
Where the name comes from
The best-known example dates back to a night at a casino in Monte Carlo in 1913, when a roulette wheel reportedly landed on black many times in a row. Gamblers lost heavily betting on red, convinced the streak had to end. Each spin, however, was independent of the last.
The fallacy is the mistaken belief that random events balance out in the short term. In reality, they only tend towards their averages over very large numbers of trials, and even then, past results do not influence the next one.
How it shows up in trading
The most common version appears after a run of losing trades. A trader thinks a winner must be coming, so they increase their position size, expecting the odds to have tilted in their favour. If the strategy’s chance of success on each trade has not changed, the run of losses tells them nothing about the next trade, except perhaps that conditions have changed and the strategy is struggling.
It also works the other way. After several winning trades, a trader may feel a loss is overdue and become hesitant, skipping good setups. Or they may decide the streak means they cannot lose, which is closer to overconfidence.
The fallacy shows up in market analysis too. Someone might argue that a share has risen for seven days straight, so it must fall tomorrow. A market that has gone up for a week can keep going up, and one that has fallen can keep falling.
Markets are not roulette wheels
There is an important difference. Unlike a roulette wheel, markets are not purely random. Trends, momentum and mean reversion are real effects that traders study. A long run of gains can sometimes precede a pullback, but if so, it is because of changes in buying and selling pressure, not because the market owes anyone a down day.
The fallacy is assuming that a streak alone shifts the odds. Good analysis looks for reasons, such as stretched valuations, changing news or fading momentum, rather than counting how many times something has happened.
Why it is dangerous
The gambler’s fallacy often leads to bigger positions at exactly the wrong time. Doubling up after losses in the belief that a win is due is the logic behind the old martingale betting system, which can wipe out an account during a long losing run. It is also closely related to revenge trading, where a trader tries to win back losses quickly and takes on far more risk than planned.
How to protect yourself
Start by thinking in terms of probabilities over many trades rather than individual outcomes. If your approach wins a certain proportion of the time, losing streaks are a normal part of it. Knowing that in advance makes them less likely to rattle you.
Keep position sizing consistent. Deciding how much to risk on each trade before a streak begins, and sticking to it, removes the temptation to bet bigger because a win feels overdue. Our guide to the risk-reward ratio shows how to think about each trade on its own merits.
Finally, when you feel a result is due, treat that thought as a warning sign rather than a signal. Ask what the evidence says, not what the streak says.
The takeaway
The gambler’s fallacy is the belief that past random results change future odds. In trading it encourages bigger bets after losses and poor judgement after wins. Treat each trade as its own decision, size it consistently and let evidence, not streaks, drive your choices.
If you want an honest view of the habits shaping your trading, our free trader assessment can highlight where to focus first.
