A flawless week. Every trade hits its target, the morning scenario unfolds as planned, and you have that rare feeling of reading the market like an open book. This is often when a retail trader makes the worst decision of the week: increasing position size.
Casino money does not exist
Croupiers have known this reflex forever. A player who has just won places a bigger bet: they feel as though they are playing with “the house’s money.” In 1990, Richard Thaler and Eric Johnson gave this behavior a name in the journal Management Science. Their experiments, conducted with real money, revealed a “house-money effect”: after a win, participants were willing to take on more risk.
The same research describes the opposite reflex. After a loss, any option that offers a chance of getting back to breakeven becomes highly tempting. The two biases go hand in hand. One pushes you to size up when everything is going well; the other makes you force trades when everything is going badly.
The mechanism behind it is mental accounting. You put the week’s profits in a separate mental bucket—the money that is “extra.” Even if you take a loss, you tell yourself, the week will still be positive. Yet one dollar won on Tuesday is worth exactly the same as one dollar deposited into your account. Your broker makes no distinction. Your brain does.
Even professionals fall for it
You might think this bias is limited to beginners. A study of independent traders on the Sydney Futures Exchange proves otherwise. Researchers compared their afternoon risk-taking based on the morning’s results. The verdict: morning gains prompted these professionals to take more risk in the afternoon.
The most telling detail? The lunch break. It should have served as a buffer—a chance to cool off. It was not enough. The authors remain cautious on one point: there is no proof that this additional risk always leads to losses. But it exposes the trader to a larger loss at the worst possible time, when vigilance is waning.
You’re winning, so you must be good?
The second driver is more subtle. It affects how you judge your own skill. Simon Gervais and Terrance Odean modeled it in a now-famous paper, “Learning to Be Overconfident”.
Their trader does not initially know how good they are. They infer it from their successes and failures. The problem is that they take too much credit for their gains: they give their successes more weight than a neutral observer would. They therefore become overconfident. According to the model, this overconfidence rises during the early years of a career, then declines with experience, when the trader finally starts to assess their true ability.
The authors add an idea every crypto trader has experienced: overconfidence rises when success is more frequent than usual across the market as a whole. In other words, a bull market manufactures geniuses. The trend does the work, and everyone thinks it was their analysis.
A winning streak does not change your statistical edge. It changes your mood—and your mood is what sets your position size.
Trade more, earn less
What does an overconfident trader do? They trade more. Gervais and Odean’s model predicts it, and the data confirms it. In their study “Trading Is Hazardous to Your Wealth”, Brad Barber and Terrance Odean tracked U.S. households investing in stocks. Those who traded frequently achieved a lower net annualized return than those who traded less. The authors see this as a sign of overconfidence, and their conclusion fits in one sentence: trading harms your wealth.
These households bought stocks outright, without leverage. In forex, index, or gold CFDs, every bout of overconfidence costs much more. The AMF study on retail investor results in CFD and forex trading found that most clients lost money. One position-size increase that gets out of hand is enough to dig this kind of hole.
The calculation your streak hides from you
On paper, sizing up after a streak seems harmless. Get out your calculator.
Scenario B is not extreme. Three losses in a row can happen with any strategy, even an excellent one. The only question is what position size you will have at that point.
Five rules for handling a winning streak
You cannot eliminate the euphoria. But you can stop it from reaching the position-size button.
- Set your position size outside market hours. Calculate your risk per trade as a percentage of capital, and recalculate it on a fixed date—for example, at the end of each month. Never during the session, and never after a win.
- Reset the counter. Before every order, ask yourself: would I take this trade, at this position size, if my day were breakeven? If the answer is no, the previous win is making the decision for you.
- Cap the number of trades. Set a maximum number per session in advance. Daily target reached? Close the platform. A good day needs protecting too.
- Earn the right to size up. Increase your risk only after a cold review, based on enough trades that the result cannot simply reflect one good week.
- Write before entering. Note in one line why you are taking the trade and why you chose that position size. A written rationale holds up better against euphoria than intuition does.
The journal, your only impartial witness
Overconfidence has one frustrating flaw: you cannot see it from the inside. You feel clear-headed, simply in good form. Only your numbers can prove you wrong.
Start by tagging each trade according to its context: was it taken after a winning streak, after a loss, at the beginning or end of the session? After a few weeks, compare the results. Does your average position size increase after three wins? Does your number of trades per day increase too? Do you follow your plan less closely? If so, you have the evidence, and it carries more weight than all your good intentions.
To avoid taking all the credit, add a column for every winning trade: did the scenario unfold as expected, or did luck save the trade, with price coming close to your stop or an unexpected announcement intervening? A lucky win should not fuel your confidence. This is exactly what Gervais and Odean describe: the bias arises from incorrectly separating skill from chance.
Doing this manually is tedious. An AI trading journal such as Edgyx automatically breaks down your statistics by context, and the Ora coach can compare your trades taken after a winning streak with the rest of your history. Ultimately, the tool matters little. What matters is reviewing these figures calmly, over the weekend—not in the middle of an euphoric session.
Key takeaways
- After a win, the brain treats profits as “casino money” and accepts more risk: Thaler and Johnson demonstrated this in 1990, and professional traders in Sydney are not immune.
- Traders too easily take credit for their gains. Their overconfidence peaks early in their careers and in rising markets.
- Overconfidence leads to more trading, and more trading is costly: in Barber and Odean’s study, the most active households earned lower returns than the least active ones.
- With leverage, the cost of an oversized position multiplies. Set your risk outside market hours and never change it after a win.
- Tag your trades by context and compare your statistics after a winning streak with the rest of your history. That is where the bias becomes visible.
