After more than 26 years as an investor, the lesson that stays with me most isn’t about a trade I got wrong. It’s about a trade I got right, and what it cost me anyway.

Walking the beach here in Naples this morning, I kept coming back to it. Because it gets at something I think is one of the sneakiest, most underappreciated risks in portfolio management:

The danger of the trade you have on that you didn’t know you had on.

If you’re not careful, it will sneak up on you and make you pay. Here’s the story that taught me that.

A Commodity Bull Market and a Very Long Commute

About three decades ago, I was working as a young analyst in downtown Baltimore, at a firm called T. Rowe Price, headquartered at the corner of Pratt and Light. I had been developing and prosecuting a thesis that China’s industrialization was creating a structural, long-term shift in demand for commodities. The cost of production was rising at the same time. In investment terms, we’d call this a secular bull market in commodities.

I had been building and expressing that thesis aggressively since roughly 2001–2003. By early-to-mid 2005, it was really starting to bear fruit. Steel prices and other materials closely tied to Chinese industrialization were showing meaningful increases. The concentric circles of rising commodity prices were widening, exactly as the thesis had predicted.

Then came Hurricane Katrina, a devastating storm that made painfully clear just how much systemic underinvestment there had been in U.S. energy infrastructure. As part of a higher-for-longer commodity thesis, it shouldn’t have been a surprise that energy prices would join the broader rally. And yet, it was in that moment that my own thesis came back to bite me. Hard.

The Hidden Trade: Short Gasoline Without Knowing It

My wife and I had chosen to live far from downtown Baltimore, on the Eastern Shore of Maryland, just across the bay from Annapolis. It was absolutely beautiful. You could watch the big boats pass under the Chesapeake Bay Bridge. We loved our time there.

The only wrinkle was the 45-to-50-mile commute to downtown Baltimore. Before we bought the house, I had done my homework and found a bus line that ran almost door-to-door between our home and my office. It was genuinely perfect: a one-hour ride each way, and with the technology of the time, BlackBerrys, early wireless, I could work the entire commute. Quality of life? Excellent. The job was world-class, the home was peaceful, the commute was productive.

And then, in the middle of a commodity bull market I had spent years engineering, they canceled my bus line.

The reason? Gasoline and diesel prices had risen to the point where the route was no longer economical. My own investment thesis, the one I had been prosecuting with conviction, had rendered my commute unworkable.

Think about what this meant practically. Suddenly, I was driving one hour each way into Baltimore, two hours a day behind the wheel, unable to work, unable to read, unable to do anything but pay attention to the road. Two hours a day over a five-day week is ten hours. A full workday, every week, lost in a car.

I was tired, cranky, and my quality of life crashed, all because I hadn’t thought through my investment thesis to its ultimate conclusion.

The Real Lesson: Think Comprehensively About Your Exposures

I still think about this episode today. It was nothing more than a natural extension of an investment view I was expressing with great conviction, but I had failed to map out all of the ways that thesis, if it worked, could affect my life and my portfolio.

This is the core risk management lesson I want to leave you with: I believe that the greatest risk you face in investing is often not the trade you’re watching carefully. It may be the consequences of that trade working, or the trade you didn’t even realize you had on.

To think most comprehensively about risk, you have to be both objective and open-minded. I believe investors should follow an investment thesis not just to the obvious conclusion, but to all of its downstream effects. Investors might ask:

• What happens if this thesis works exactly as I expect?
• What are the second and third-order effects of that success?
• Are there hidden positions in your portfolio or your life that become liabilities if the thesis plays out?

I had the right thesis. I just didn’t think comprehensively enough about all the ways it would play out, including the one that cost me ten hours of free time a week.

Don’t make the same mistake I did. Think more deeply than I did and don’t let the trade you have on that you didn’t know you had on sneak up on you like it snuck up on me. 

Hang in there.