Overconfidence Bias in Stocks: Why Winning Streaks Make Traders Lose Money

Three trades, three wins. On the first one you were careful: small position, tight stop loss. By the second you started to relax. By the third, your brain was already whispering, "I've actually got a talent for this." So on the fourth trade you size up hard, drop the stop loss, and feel certain the market will move exactly as you predicted. Then the stock turns, and in a single blow you lose more than the combined profit of your three previous wins.

If that story feels a little too personal, you have just met one of the quietest capital killers in trading: overconfidence bias. The irony is that it does not attack weak traders. It attacks traders who have just won.

What Is Overconfidence Bias?

Overconfidence bias is the human tendency to rate your own ability, knowledge, and forecasting accuracy far higher than reality warrants. In a stock market context, it means you believe you can read the market better than you actually can, then take on risk whose true size you do not even register.

Here is the short answer: overconfidence bias turns healthy confidence into costly arrogance. The difference between a confident trader and an overconfident one is not in today's result, but in the size of risk they are willing to take without realising it. According to Investopedia, this is among the most studied psychological errors in behavioural finance because its effects are consistent across markets and cultures.

What makes it dangerous: overconfidence does not feel like a mistake. It feels like competence. You feel you have "figured the market out," when what really happened is that you got lucky a few times in a row.

Why Three Wins in a Row Are Dangerous

Winning streaks are poison wrapped as a gift. Every time you profit, your brain releases dopamine and draws a flawed conclusion: "this profit came from my skill." This is called self-attribution bias - we take full credit for wins, but blame the market, the news, or bad luck for losses.

The problem is that in the short term, a large part of trading outcomes is driven by randomness. Three wins in a row no longer prove you are skilled than flipping a coin and getting "heads" three times makes you a coin-flipping expert. But the human brain is very poor at telling real skill apart from short-term luck.

The damage then unfolds in two stages. First, you start increasing your position size because you are sure "this one will work." Second, you start loosening your discipline - dropping stop losses, ignoring your analysis, and entering trades with no clear setup. That combination of bigger positions and looser discipline is the exact formula for one large loss erasing many small wins.

The Psychology: Illusion of Control and Self-Attribution

Overconfidence bias grows from two deep psychological roots. The first is the illusion of control - the feeling that we can influence outcomes that are genuinely beyond our control. When you spend hours reading charts and news, your brain assumes that effort should translate into control over price movements. The reality is that the market does not care how long you have studied.

The second is self-attribution bias. Research in behavioural finance journals, including a study published on ScienceDirect on overconfidence bias and investment performance, finds that overconfident investors tend to take on more risk and trade more frequently, yet earn lower returns on average. They confuse activity with progress.

The combination of these two biases produces a trader who feels "in control" while really just riding a slow, random wave that will eventually reverse.

The Real Cost: Overtrading and Reckless Position Sizing

The cost of overconfidence is not abstract - it can be measured. The classic study by Brad Barber and Terrance Odean, titled "Trading Is Hazardous to Your Wealth," analysed tens of thousands of retail investor accounts and found that the investors who traded most frequently earned the lowest net returns. The main cause: overconfidence drives overtrading, and every trade adds transaction costs and a fresh chance for an emotional mistake.

Locally, this cost shows up in several forms:

• Reckless position sizing - instead of risking 1-2% of capital per trade, the overconfident trader suddenly stakes 20-30% because "this one is a sure thing."
• Dropping the stop loss - because they are sure the price will recover, even though the stop loss is the only wall against a large loss.
• Averaging down with no thesis - adding to a falling stock purely out of refusal to admit being wrong.
• Margin and leverage - using borrowed money because returns feel guaranteed, so a single adverse move can wipe out the entire capital.

Each of these behaviours looks reasonable while you are winning. That is precisely the trap.

Signs You Have Become Overconfident

Overconfidence rarely comes with a clear warning. But there are signs you can watch for in yourself:

• You start increasing position size after every win - not because of a system, but because of a "feeling."
• You stop keeping a trading journal because you feel you "already know what you're doing."
• You begin ignoring the stop losses you set yourself.
• You trade more often than usual, sometimes without a clear setup.
• You start believing you are "different" from the majority of investors who lose.
• You share forecasts with full confidence on social media and feel obligated to prove them right.

If three or more of these appear after a string of wins, you may be riding overconfidence - and the market is preparing a lesson.

From Demo Account to Real Account: The Overconfidence Spike

One of the most common entry points for overconfidence is the move from a demo account to a real one. A new trader might trade a demo account for a few weeks, watch the virtual balance climb, and conclude they have mastered the craft. The problem is that a demo account does not test the single most important variable: your emotions when real money is on the line.

In a demo account, you can take losses without pain, so your decisions stay calm and rational. When you switch to real money, emotional pressure changes everything - hands shake as the price drops, and the temptation to drop the stop loss becomes overpowering. The confidence built in a risk-free environment is exactly what tends to collapse in the real world.

The lesson here is not to avoid demo accounts, but to understand that demo success is not the same as real skill. Start a live account with a very small position, and let the market test your discipline before you size up.

A Real Example on Bursa Malaysia

Look no further than the rubber glove euphoria of 2020. When the share prices of glove makers surged several fold, many new investors who bought early and profited heavily began to believe they had the golden touch. They added to positions at ever-higher prices, some using margin, certain the trend would never end. When prices finally reversed and fell in stages, many gave back their gains - and worse still were those who entered late with large positions.

The same pattern repeats in every wave of speculation - from tech stocks to crypto to penny stocks that go viral on social media. InvestSmart by the Securities Commission Malaysia repeatedly reminds retail investors not to get swept up by momentum and crowd confidence. Tellingly, the biggest victims are usually not investors who always lose, but those who win first and then become too confident.

Overconfidence vs Healthy Confidence: Where Is the Line?

It is important to understand that confidence itself is not the enemy. Without confidence, you would never pull the trigger on a good setup. The problem is not confidence - it is confidence that is not measured against risk.

Healthy confidence sounds like: "This setup meets my criteria, so I enter with 1% of capital at risk and a stop loss at level X." Overconfidence sounds like: "I am sure this stock is going up, so I go in big and don't need a stop loss." The first respects uncertainty; the second denies it.

Professional traders actually operate with a healthy dose of doubt. They know every trade is just a probability, not a certainty. This is why risk management, not forecasting accuracy, is what separates traders who last from those who burn out after a few months.

How to Beat Overconfidence Bias

You cannot delete overconfidence entirely because it is wired into the human brain. But you can build systems that protect you from it:

• Set firm position sizing rules. Limit risk per trade to 1-2% of capital, and do not change this rule just because you are winning.
• Keep a trading journal. Record your reason for entering every trade. After a month, you will see how many of your "wins" were actually luck, not skill.
• Separate decisions from outcomes. A good trade can lose, and a bad trade can win. Judge the quality of your decision, not just its result.
• Use a pre-trade checklist. If a setup does not meet every criterion, you do not enter - no exceptions, even when you feel "sure."
• After a winning streak, reduce size. This is counterintuitive, but it protects you precisely when you are most exposed to overconfidence.
• Seek the opposing view. Before going in big, force yourself to list three reasons you might be wrong. This directly counters the illusion of control.

This discipline is not exciting, which is exactly why most traders ignore it - until the market forces them to learn it the expensive way.

Overconfidence and the Family of Mental Biases

Overconfidence bias rarely travels alone. It teams up with other mental biases to trap you. Confirmation bias makes you read only the news that supports your belief. Anchoring bias holds you to your original buy price so you refuse to exit even when the thesis has changed. Recency bias makes you assume recent wins will continue forever.

The combination of these biases forms a dangerous cycle: you win a few times (recency), you take full credit (self-attribution), you only seek supporting information (confirmation), and you go in big without a stop loss (overconfidence). Understanding that these biases reinforce each other is the first step to breaking the cycle.

Frequently Asked Questions (FAQ)

What does overconfidence bias mean in trading?
It is the tendency to rate your own ability and forecasting accuracy higher than reality, then take on larger risk than you should without realising it.

Why does overconfidence bias always strike after a win?
Because winning releases dopamine and triggers self-attribution bias - the brain takes full credit for success even when part of it is luck, then raises confidence unrealistically.

Is confidence in trading a bad thing?
No. Confidence measured against risk management is necessary. What is dangerous is confidence that denies uncertainty and ignores stop losses and position sizing.

How does overconfidence cause large losses?
It drives overtrading, reckless position sizing, and dropping stop losses. One large loss under these conditions can erase many small previous wins.

Can overconfidence bias be eliminated completely?
No, because it is part of human psychology. But its effects can be controlled with systems such as checklists, a trading journal, and firm position sizing rules.

What is the first step to fighting overconfidence?
Keep a trading journal and separate the quality of your decisions from their outcomes. This helps you see how many wins were actually luck rather than skill.

Conclusion

Overconfidence bias is the reason many talented traders still end up losing. It does not attack when you are weak, but precisely when you are strongest - after a few wins that build the illusion you have mastered the market. The truth is that the market respects no one's ego, and short-term wins are not proof of long-term skill.

Traders who last are not the most confident, but the most disciplined about respecting uncertainty. They know that protecting capital matters more than proving themselves right.

The first step to investing more wisely is building a system that protects you from your own confidence. For that, you first need the right account.

Open a CDS and trading account to start investing on Bursa Malaysia as well as foreign stocks such as the United States and Hong Kong markets.

If you are just starting out and want to understand the fundamentals of stock investing more deeply, download our free stock market basics ebook as your starting point.

Further Reading

• Recency Bias in Stocks: Why Traders Assume Yesterday's Trend Will Continue Tomorrow
• Confirmation Bias in Stocks: Why You Only Read News That Agrees With You
• Anchoring Bias in Stocks: Why Your Brain Clings to the Original Buy Price
• Investor Psychology: 7 Mental Biases That Make You Lose Money on Bursa Malaysia
• Is Stock Trading Just Gambling? 5 Sharp Differences Between Investors, Traders and Gamblers