Education
"Diversification" Doesn't Mean What Most New Investors Think It Means
Owning ten different stocks feels diversified. Owning ten stocks in the same sector that all move together on the same news isn't — the number of positions was never really the point.
A common misconception treats diversification as simply a matter of owning more things — ten stocks feels safer than two, the thinking goes, purely by virtue of the count. That's not quite what diversification actually measures; what matters is how correlated those ten positions are with each other, not how many of them there are.
Ten different technology stocks can move almost in lockstep during a sector-wide selloff, providing barely more protection than holding one of them at a larger size — the number of tickers went up, but the actual risk reduction that diversification is supposed to provide didn't materialize, because all ten shared the same underlying exposure to the same sector-wide risk.
Genuine diversification comes from combining assets that don't move together for the same reasons — different sectors, different asset classes (stocks alongside bonds or commodities), or different geographies whose economic cycles aren't perfectly synchronized. Two positions with low correlation to each other can reduce overall portfolio volatility more than ten highly correlated ones, even though the second portfolio has far more line items.
The practical test worth applying to a portfolio isn't "how many different things do I own" but "how many genuinely different things are actually driving these positions" — a distinction that's easy to state and surprisingly easy to overlook when building a portfolio one familiar-sounding name at a time.