Why Concentration Drives Outsized Returns
- cameronhayes11
- Apr 25
- 4 min read
The conventional investment wisdom is clear: diversify. Own as many stocks as possible across as many sectors as possible. Spread the risk. Don't put too many eggs in one basket.
The investors with the best long-term records—Warren Buffett, Charlie Munger, Mohnish Pabrai, Nick Sleep, Joel Greenblatt—have largely ignored this advice.
This is not contrarianism for its own sake. It's a coherent argument, backed by mathematics and decades of empirical evidence, that a concentrated stock portfolio of genuinely great businesses produces better outcomes than a broadly diversified portfolio of mediocre ones. Here's why.
The Mathematics of Concentration
Start with the arithmetic. Suppose you find a stock that goes up 10x over five years—a genuine ten-bagger, rare but real.
If it's a 1% position in a 100-stock portfolio, that ten-bagger contributes 9% to your total portfolio return.
If it's a 7% position in a 15-stock portfolio, that same ten-bagger contributes 63% to your total portfolio return.
Same investment insight. Same research. Same conviction. Entirely different portfolio outcome, created entirely by how much of your portfolio you allocated to the idea.
This is the fundamental problem with excessive diversification: your best ideas don't matter. You can be right about a business in a profound, well-researched, high-conviction way—and because the position is 1% of your portfolio, it barely moves the needle. Meanwhile, your 70 least-certain positions—the ones you own primarily for diversification—collectively drag on performance without adding meaningful information or genuine risk reduction beyond what you'd get from 15 positions.
What the Best Investors Actually Do
Warren Buffett's early partnerships were significantly concentrated. His position in American Express in 1963-64 represented roughly 40% of his partnership's assets. He understood the business, assessed the crisis as temporary, and sized the position to reflect his conviction. The result was one of the most profitable investments of his career.
Buffett has articulated the logic directly: "A policy of portfolio concentration may well decrease risk if it raises, as it should, both the intensity with which an investor thinks about a business and the comfort-level he must feel with its economic characteristics before buying into it." The constraint of concentration is itself a discipline. When you know you can only own 15 businesses—not 150—you become dramatically more selective.
Charlie Munger's characterisation: "The idea of excessive diversification is madness. To me, it's obvious that the winner has to bet very selectively. It takes character to sit there with all that cash and do nothing." Concentration requires the patience to hold a small number of positions while staying inactive in the face of hundreds of other apparently interesting opportunities.
Nick Sleep and Qais Zakaria, whose Nomad Investment Partnership compounded at roughly 20% annually from 2001 to 2013, typically held 10–15 positions. Their core holding for much of that period was Amazon—recognised early, held with conviction through years of volatility and skepticism. The concentrated position in Amazon alone drove a substantial portion of the fund's extraordinary returns. A broadly diversified fund holding Amazon at 1% would have received only a fraction of that benefit.
The Problem with Adding Your 51st Stock
When does adding another stock actually improve your portfolio?
The statistical answer is well-established: most of the benefit of diversification—reduction in single-stock idiosyncratic risk—is captured by the first 10–15 holdings. After that, each additional stock contributes negligible additional diversification benefit.
More practically: what quality are your 51st and 52nd stocks relative to your 1st and 2nd? If you genuinely believe stocks 1 and 2 are significantly better investments than stocks 51 and 52, why are you diluting the portfolio with lower-quality ideas?
Peter Lynch called this "diworsification"—a portfolio that expands beyond genuine high-conviction ideas and gets filled with mediocre investments that dilute returns while giving only the appearance of diversification. A portfolio of 80 mediocre businesses, each compounding at roughly the market average, is diversified but uninspired. A portfolio of 12 exceptional businesses, each compounding at 15%+ ROIC with genuine competitive advantages, held at conviction-weighted sizes, is concentrated—and potentially excellent.
When Concentration Requires
Concentration doesn't work without its prerequisites.
Concentration only creates the promised outperformance if the concentrated positions are businesses you genuinely understand better than the average market participant. If you're concentrating in businesses you understand no better than anyone else, you're merely taking more idiosyncratic risk without the competence to be compensated for it.
The Horse Racing Analogy
Think of it like betting on horse races. You've studied the horses intensively. You believe one of them is significantly more capable than the others—better training, better form, better conditions. The rational strategy is to bet heavily on that horse.
If you spread your bets equally across all 10 horses to "diversify your risk," you're guaranteed a result near the average. You'll win a bit on some horses and lose a bit on others. The 10-horse strategy eliminates your edge entirely—the edge you built through intensive analysis of which horse is genuinely best.
Spreading your bet equally across all horses only makes sense if you believe you can't distinguish between them. And if that's true, you probably shouldn't be at the track at all.
Stock investing is the same. If you genuinely believe stocks 1 through 5 are significantly better than stocks 46 through 50, your portfolio should reflect that. Treating them equally is an implicit admission that you either can't distinguish between them, or you don't have the conviction to act on the distinction.
The Practical Framework
A practical approach for individual investors:
For the position sizing framework that makes concentration practical, see position sizing as the ultimate edge. And for the portfolio composition question this all leads to, see how many stocks should I own in my portfolio.
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The content on Gingernomics is for educational and informational purposes only and does not constitute financial advice. Always do your own research and consult a licensed financial advisor before making any investment decisions.
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