Some of your biggest mistakes will be stocks you made money on One of the most dangerous things that can happen to an investor is getting rewarded for a bad decision. A loss forces you to think. A lucky win can convince you that you never needed to. You buy something you barely understand because it is going up. The valuation makes no sense, the business is mediocre and your thesis is mostly narrative. Then the stock doubles and suddenly the market has taught you that bad behavior works. That is how investors get into trouble. Not always through one gigantic mistake, but by being rewarded for lowering their standards. The market can reinforce bad habits for a long time before punishing them. This is why making money and being right are not the same thing. The market can give you a great result even when your analysis was wrong. That matters far more than most investors realize. Imagine buying a company because you believe earnings will double in 3 years. Earnings barely move, but the valuation goes from 15 times to 30 times and the stock doubles anyway. You made money, but your thesis failed. Maybe you bought a highly leveraged business because you expected debt to fall quickly. Debt barely moves, interest rates decline and the market stops caring. Again, you made money, but not for the reason you expected. Your brokerage account records a win. Your investing journal should record something different. That is difficult for most investors to admit. This is why every investor should keep two scorecards. The first is obvious, what return did I make? The second is more important, how much of my original thesis actually came true? Did revenue develop the way I expected? Did margins improve for the reasons I expected? Did free cash flow grow, did the moat strengthen and did management allocate capital well? If most of those answers are no, I do not care how green the position was. I got paid, but I did not necessarily invest well. Those are two different things. The reverse is also true. You can buy a great business at a sensible valuation, have the thesis play out and still watch the stock fall 30% because the multiple compresses. That can feel like failure even when your process was excellent. This matters because investing is a repeated game. You are not trying to be right once. You are trying to build a process that survives decisions over decades. A bad process that makes money is dangerous because it encourages repetition. Every time it works, confidence increases. Eventually you take bigger risks with worse ideas because the market trained you to believe your process was better than it was. This is why bull markets can make investors worse. Weak businesses look good, bad valuations feel justified and aggressive decisions seem intelligent. The market rewards behavior that would look foolish in a harder environment. You stop asking whether your reasoning was correct. You start asking whether the stock went up. That is where investing can turn into something else entirely. Price can validate your ego long before it validates your thesis. Sometimes the most dangerous investor is not the one who lost money. It is the one who made a lot of money for reasons they do not fully understand So after a winner, I ask myself something uncomfortable. If the stock had fallen 30% instead of rising 50%, would I still believe my analysis was good? Could I still defend the thesis without pointing to the stock price? If the answer is no, maybe the stock did not prove I was right. Maybe the price simply prevented me from discovering I was wrong. That is an important difference Some of your biggest investing mistakes will never appear as losses. They will appear as profits that taught you the wrong lesson. Those can become the most expensive profits you ever make If you enjoy my writing, consider subscribing for deeper research, private ideas, Q&As and more direct access to me. My investing book is also coming around Christmas🌹