Overconfidence

### Why a streak lies to you Overconfidence does not feel like arrogance. It feels like clarity. That is what makes it hard to catch in the moment. Gervais and Odean modelled exactly how it forms in *Learning to Be Overconfident* (Review of Financial Studies, 2001). A trader does not know his own ability, so he infers it from his successes and failures, and, in their words, "In assessing his ability the trader takes too much credit for his successes." The model's sharpest result is the one nobody wants: "A trader's expected level of overconfidence increases in the early stages of his career." Only later, with more experience, does he come to better recognise his own ability. So the most dangerous version of you is not the beaten-up one. It is the one who has just found something that works and has not yet lived through a regime that breaks it. Winning streaks feel like skill, but they are usually skill plus variance plus a market regime that happened to suit your setup. Two of those three can leave without telling you. ### What it actually does to behaviour The central prediction of overconfidence theory is simple: overconfident traders trade too much. The best-known real-world test is Barber and Odean's *Boys Will Be Boys* (Quarterly Journal of Economics, 2001), using account data for more than 35,000 households from February 1991 through January 1997. Men traded 45 percent more than women and earned annual risk-adjusted net returns 1.4 percent lower. Among single accounts the gap widened: single men traded 67 percent more than single women and earned risk-adjusted net returns 2.3 percent lower. Gender was only a proxy for overconfidence there. The point is not about men. It is that the group that felt more certain traded more, and kept less. ### The size-up is where the damage happens The streak itself does not hurt you. The size-up that follows it does, and it never announces itself as recklessness. It arrives as a reasonable-sounding sentence: *I'm reading this market well right now.* Do the arithmetic on your own scale. Five wins at 1R each puts you 5R up. Treble your risk on the sixth trade and lose it, and 3R of that run is gone in one click. Do it twice and the whole run is gone, and then some, leaving only the confidence it bought you, which turned out to be the expensive part. The cure is structural, not emotional. **Fixed-percentage risk** makes your position size a function of your account balance, not of your mood. The moment you size by conviction, confidence becomes the thing that sets your risk, and confidence is precisely the variable that spikes right before it should not. Write the number down when you are calm. Then ignore the last 10 trades entirely, because the market has no idea you are on a run.