It was a Tuesday in March and I was feeling sharp. Four positions open, all in different tickers — energy, materials, a couple of mid-cap miners. On paper it looked like a diversified book. In reality I'd built one enormous directional bet on commodity sentiment and dressed it up in four different jerseys. The market didn't care about my wardrobe.

The thesis on each trade was slightly different, which is exactly what made it feel legitimate. One was a breakout play. One was a mean-reversion setup. Two were momentum signals from the algo. But underneath all four was the same assumption: that risk appetite would hold. When it didn't, every single position moved against me simultaneously. I watched four separate stop-losses trigger inside eleven minutes.

CONCEPTCorrelation measures how closely two assets move together — when it's high, multiple positions behave as one.
WARNINGHolding multiple correlated positions multiplies your real risk exposure, not your diversification.
KEY IDEATrue diversification requires uncorrelated return streams — different setups on the same theme don't qualify.

The root cause wasn't greed. It wasn't overconfidence in any single trade. It was a failure to measure the actual correlation between positions before sizing them. Each trade passed my individual risk filter. None of them passed a portfolio-level correlation check — because I hadn't built one. I was running four trades but carrying the drawdown risk of one very large trade.

Portfolio Drawdown: Correlated vs Uncorrelated0-5%-10%-15%Event+1 day+2 daysCorrelated bookUncorrelated book

The one rule I pulled from this: before entering any new position, calculate its correlation coefficient against everything already open. If the aggregate exposure to a single macro theme exceeds a set threshold, the trade doesn't go on — regardless of how different the setup looks. Understanding correlation and dependence at a portfolio level is what separates position sizing from wishful thinking. Traders also use portfolio variance calculations to quantify exactly how much combined risk correlated holdings actually carry.

Four different tickers, one catastrophic assumption. The diversification was cosmetic.

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