Why We Sell Stocks Too Early (and How to Fight It)

You're sitting in front of the monitor, your heart beating a bit faster than usual, and the screen shows a green number: +18%. A wild dialogue immediately starts in your head: “What if it crashes tomorrow? I'd better sell it now, a profit in the account is a sure thing!” You click, sell, a wave of relief washes over you, and you feel like a small-scale Warren Buffett. A year later, you look at that stock again — it's up by half, and you're not there.

Almost every investor knows this moment. It's one of the most expensive reflexes we have in our heads — and yet it seems perfectly right.

A Scene We All Play

A model example. An investor buys shares of a tech company for 100,000 Kč, having done thorough homework. Over eighteen months, the company reports excellent results, and the position's value grows to 135,000 Kč — a 35% increase. Joy, adrenaline, and especially that gripping feeling: “No one must take this from me.” They sell. A profit of 35,000 Kč, a glass to celebrate.

The problem is that the company was just beginning its best chapter. It continued to dominate its sector, increased free cash flows, and its intrinsic value steadily grew. A few years later, the original position would be worth several times more — but our investor had long since exited at the first stop. The profit they secured was real. The profit they missed out on was significantly larger. And that often hurts more than a loss.

This is classic: we pick the flower before it fully blooms.

What's Happening in Our Heads

Several well-described psychological mechanisms are behind premature selling. We're not stupid — we're just poorly programmed for the markets.

Reverse loss aversion. Behavioral research (notably the work of Kahneman and Tversky) shows that we perceive the pain of loss about twice as strongly as the joy of an equivalent gain. With a rising position, it reverses: we have a panic fear that the paper profit will disappear again. We sell to preemptively turn off the pain of a possible "return."

Disposition effect. Statistically, investors tend to sell winners too early and hold onto losing positions too long. Exactly the opposite of what would make sense. Analyses of retail investor behavior confirm this pattern across markets and time periods.

The need to be right. A realized profit is like a report card with an A. It reassures us that we made the right decision. The brain loves closed stories with a happy ending — and an open position has no end, only uncertainty. Selling at a loss would mean admitting a mistake, which the ego is reluctant to allow. We prefer to tell ourselves that "as long as I don't sell, I haven't really lost anything."

Anchoring to the purchase price. We fixate on how much we bought for. "It's 35% higher, that's a lot." But the market doesn't care what you bought for. The price rises or falls based on the business, not your entry anchor.

Data Block: What Research Shows and Why a Few Big Winners Matter

Now the important part, orientationally and descriptively. A pioneering study of the disposition effect was conducted by behavioral economist Terrance Odean, who analyzed tens of thousands of real investor accounts. The finding was rather harsh: investors sold their winning stocks significantly more often than their losing ones. And when scientists tracked what happened next, it turned out that prematurely sold "winners" performed better on average in the following year than the positions investors held onto in hope of a turnaround. In other words — we were picking flowers and watering weeds.

Another unpleasant truth from long-term stock market studies: most of the total index return comes from a small minority of stocks. Extensive historical analysis of the U.S. market over roughly nine decades found that a large portion of companies throughout their existence did not even outperform the returns of short-term government treasury bills. Conversely, the vast majority of net value creation was generated by only a small percentage of stocks — a few percent of all companies.

What does this mean for us who like to sell early? That one position you picked with a nice profit could theoretically be exactly the type of stock that makes up most of the long-term result. When you cut it off at the start, you cut yourself off from the narrow group of winners on which the entire math of investing stands. In terms of probability: you cut off the right side of the distribution curve.

Practical Framework: How to Stop Picking Winners Too Early

Now the actionable part. You don't need iron willpower, you need pre-set rules so that in a moment of adrenaline, your amygdala doesn't make the decision.

1. The Reverse Table Test. Before selling just because you're in the black, ask yourself: “If I held cash of this value today, would I buy these shares at the current price?” If yes — because the business is still doing great — you have no rational reason to sell.

2. Divide the reasons for selling into two piles. Good (fundamental) reasons: the thesis broke (the company stopped growing, the competition overtook it, management allocates capital dubiously), you need the money, or the position has grown so much that it disrupts your risk management. Bad reasons: “I'm afraid it will fall,” “it's high enough,” “I have to finally secure it.” Ask yourself: am I selling because of the company, or because of my nerves?

3. Write down the purchase thesis right at the purchase. In a note, write in three sentences: why I have this stock and what would convince me that I was wrong. Then you sell only when the thesis breaks — not when your hand shakes. It's simple and brutally effective.

4. Consider selling in parts (scale-out). Instead of an "all or nothing" decision, you can lighten the position in pieces. If you sell, say, a third, you fulfill the need to “secure something” and let the rest continue to work. Psychologically, it works great — you calm the fear without leaving the whole story.

5. Take a 24-hour break before selling. A joyful sale of a winner is as impulsive as a panic sell at a loss. If you take a day to think it over, the adrenaline subsides, and the brain, not reflex, makes the decision.

6. Track how much you "left on the table." Keep a simple sales diary: what you sold, for how much, and where the stock is a year later. It's not self-flagellation — it's training. After a few entries, you'll see your own pattern in black and white, and that heals better than any lecture.

In QMA

The problem of premature selling is largely an informational problem: we sell out of fear because we don't see if the company is still "running." In QMA, scores and fundamental metrics of the position serve this purpose — instead of the feeling "it's somehow too high," you see descriptively whether the company's business is still growing or breaking. And a watchlist with a note keeps your original thesis in sight, so with every bout of nerves, you can check if something really broke or if you're just scared. QMA helps separate short-term noise from real changes in intrinsic value — but the decision remains yours.

What to Take Away

• Write down the purchase thesis today for one position you hold: why I have it and what would convince me that I was wrong. Sell according to this sentence, not your nerves.
• Use the reverse table test — a price increase of 20% or 50% alone is not a reason to sell if the business under the hood is still growing healthily.
• Implement a 24-hour pause before every "joyful" sale of a winner and try selling in parts instead of "all or nothing."
• Start a sales diary and occasionally check where those stocks ended up. Your own pattern will teach you more than ten articles.

Past performance is not a guarantee of future results.*