How many positions to hold isn't a technical detail settled by some rule of thumb. It's a statement about how much an investor trusts their own judgment.
How many holdings a portfolio should contain usually gets treated as a technical matter, settled by some rule about the minimum count needed for adequate diversification. That treatment misses what the question really is. Deciding on concentration is deciding how much you trust your own judgment, and it deserves to be recognized as such, because that's the actual stake on the table.
The case for concentration is coherent, and serious people have made it. If an investor has genuinely identified a small number of excellent opportunities, and the analysis behind them is sound, spreading capital across many more holdings just means funding the weaker ideas too. Diversification, on this view, dilutes your best thinking, and nobody holding fifty positions can actually know fifty businesses well. Concentration buys depth of understanding, and depth of understanding is where the edge comes from in the first place.
The case for diversification is equally coherent, resting on a different premise: individual judgments are less reliable than the people making them tend to believe. Even careful analysis can be wrong for reasons the analyst never saw coming - a business undone by an unforeseen event, a fraud, a technological shift arriving faster than expected. Diversification isn't a confession of ignorance about any specific company. It's an acknowledgment that the future is genuinely uncertain and that no analysis, however good, erases that uncertainty.
So the choice turns on something most investors are poorly equipped to judge honestly: how good their own analysis actually is. Concentration suits someone whose judgment is genuinely reliable, and who has the resources and temperament to survive the times it isn't. Diversification suits everyone else. The catch is that the confidence needed to concentrate is exactly the confidence bad analysts also carry around, and it tells you nothing about which group you're in.
The asymmetry of outcomes deserves attention, because it's what makes this decision serious rather than merely academic. A concentrated investor who's right can do extremely well. A concentrated investor who's wrong can take a loss the portfolio never recovers from within any horizon that matters. A diversified investor who's right does moderately well, and one who's wrong absorbs the mistake and keeps going. These aren't mirror-image distributions, and an investor honest about the chance of catastrophic error should weight the downside more heavily than symmetry would suggest.
There's a version of concentration that isn't a choice at all but an accident, and it's common enough to name. An investor may hold what looks like many separate positions and still be concentrated in a single underlying exposure, if those positions all lean on the same industry, the same economy, or the same set of conditions. Diversification by headcount isn't diversification by substance. Own twenty companies that would all get hit by the same event, and you hold one position expressed twenty different ways - and you may not find out until the event actually arrives.
For most investors the reasonable middle ground isn't a specific number but a principle: hold enough that no single mistake can be ruinous, and few enough that you can genuinely understand what you own. That's deliberately vague, because the right figure depends on your circumstances, your horizon, and an honest read of your own analytical reliability that only you can make. A rule handed down as a universal number is a rule that stopped thinking about the actual question.
The core-satellite structure covered elsewhere in this series offers one practical resolution to the tension, allowing broad diversification in the core while leaving room for concentrated conviction in a bounded slice. It doesn't eliminate the underlying question, but it makes the answer safer by letting concentration express judgment without staking everything on it.
One thing that often settles the question in practice has nothing to do with analytical skill: what a severe loss would actually mean for the investor's life. Two people can share identical judgment and reach identical conclusions, and yet concentration might be entirely reasonable for one and reckless for the other, simply because one can absorb being wrong and the other can't. An investor with substantial other resources, a long horizon, and no foreseeable need for the money sits in a different position from one whose portfolio is their entire financial security. The analysis hasn't changed. The cost of being wrong has. That's why the question of how much to concentrate can't be answered by looking at the opportunity alone, and why any advice that recommends a concentration level without knowing the recipient's circumstances has skipped the most important variable in the whole calculation.
At VESTFY™, this question is framed as honest self-assessment rather than a technical setting. An investor who concentrates should be able to say why they believe their judgment is reliable enough to justify it, and should treat any difficulty answering that as information in itself. Humility isn't a weakness in an investor - it's frequently what keeps them around long enough to benefit from the calls they do get right. Surviving your own errors is the precondition for everything else, and diversification, underneath it all, is simply a structural expression of that fact.