Why Most Stocks Lose Money — and What That Means for Your Portfolio

"Do not put all your eggs in one basket" is repeated so often that it has stopped carrying information. The case for diversification is far more specific than a proverb, and considerably more startling.

The study

Hendrik Bessembinder examined every common stock listed in the United States from 1926 onward and published the results in the Journal of Financial Economics in 2018. Two findings stand out.

Roughly four out of every seven stocks — about 57% — delivered lifetime returns below one-month Treasury bills. The majority of individual stocks did worse than the closest thing to a risk-free asset.

The best-performing 4% of listed companies account for the entire net wealth creation of the US stock market over that period. The other 96%, collectively, matched Treasury bills. More strikingly still, the top 90 companies — around one-third of one percent of the total — produced more than half of all the wealth created.

What this actually means

Stock market returns are not spread evenly. They are enormously skewed: a small number of extraordinary winners carry everything, while the typical stock is mediocre and a large minority are outright losers.

The average is excellent. The median is not. And when you buy a handful of individual stocks, you are far more likely to end up with the median experience than the average one.

This reframes the diversification argument entirely. The usual version is defensive — spread your holdings so no single failure hurts too much. The stronger version is offensive: you diversify to make sure you own the winners, because a handful of them produce nearly all the return, and identifying them in advance is extraordinarily difficult.

A ten-stock portfolio is not simply riskier than the index. It is statistically likely to miss the few companies that mattered.

The arithmetic of concentration

The defensive case still holds. If a single position falls 60%:

• At 50% of your portfolio, you lose 30% overall
• At 25%, you lose 15%
• At 10%, you lose 6%

And losses are asymmetric in a way gains are not. A 50% loss requires a 100% gain to recover. A 30% loss requires 43%. Avoiding large drawdowns matters more than capturing large gains, because the mathematics of recovery is unforgiving.

Concentration you did not choose

Several common situations create concentration people do not think of as a decision:

Employer shares. If a meaningful share of your wealth is in the company you work for, your salary and your savings depend on the same organisation. A bad enough year takes both at once. This is the least diversified position it is possible to hold, and it is extremely common.

Home-country bias. Investors everywhere hold far more of their domestic market than its share of global markets warrants. If you also live, earn and own property in that country, your entire financial life is one economy.

Sector clustering. Owning eight technology companies is not eight positions. They rise and fall together, and in a sector downturn they behave much like one large position.

Property. For many households the home is the dominant asset — a single, illiquid, undiversified holding in one city.

What diversification does and does not do

It does not eliminate risk. In a broad market decline, nearly everything falls together, and diversification will not prevent that.

What it removes is specific risk — the risk that one company's fraud, product failure or bankruptcy destroys a large part of your wealth. That is the risk you are not compensated for taking, because it can be diversified away for free.

Market risk is the risk you are paid to bear. Single-company risk is the risk you bear for nothing.

Practical implications

• Broad index funds solve most of this cheaply. They own the winners by construction, without requiring you to identify them.
• Diversify across geographies, not only across companies.
• Treat employer shares as a concentration to manage, and reduce them when you are able.
• If you want to pick individual stocks, size the position accordingly. There is nothing wrong with holding a few convictions — but at a weight where being wrong is survivable.
• Count sectors, not just holdings. Twenty positions in one industry is one bet.

The uncomfortable conclusion

The Bessembinder findings are difficult to sit with, because stock picking is enjoyable and index funds are dull. But the data says the median stock is a poor investment, the mean is carried by a few extraordinary ones, and your odds of holding enough of those with a concentrated portfolio are not good.

Owning everything is not an admission of defeat. Given how the returns are actually distributed, it is the position the evidence supports.

Source: Hendrik Bessembinder, "Do Stocks Outperform Treasury Bills?", Journal of Financial Economics, 2018.