Most investors make one mistake before they ever buy a stock: they assume the future will look like their forecast. But a one-page memo written inside the Pentagon in 2001 shows why even the best-informed people in the world routinely get the next decade wrong — and what that means for your portfolio today.

In the spring of 2001, a Pentagon official named Lin Wells was asked to contribute to the Quadrennial Defense Review. For half a century, the method was to predict the threat and build against the prediction. The expected deliverable was a forecast. Wells handed in a single page , since declassified, and it may be the best one-page argument about the future ever written.

Instead of predicting the next decade, he reviewed the previous 10. If you had been a security policymaker in the world's greatest power in 1900, he wrote, you would have been British, watching your age-old enemy, France. Ten years later, France is your ally and the enemy is Germany. Decade after decade, the best-informed people alive, backed by the largest intelligence apparatus ever assembled, got the 10-year picture wrong.

Then his closing line: "I'm not sure what 2010 will look like, but I'm sure that it will be very little like we expect, so we should plan accordingly."

The 2001 Quadrennial Defense Review formally shifted the department from threat-based planning to what it called a capabilities-based approach. In plain language: stop building the force around a specific enemy you have predicted. Build capabilities broad enough to handle threats you cannot predict. The report went to Congress, over Rumsfeld's signature, dated Sept. 30, 2001. Nineteen days before it was delivered, the future it was warning about arrived. The department has planned around uncertainty ever since.

Is Your Portfolio Built For One Future Or Many?

Look at your portfolio. Is it built to sink or swim on a single prediction?

Here’s the challenge: portfolios built around a prediction, when right, produce spectacular returns. Situational Awareness, the hedge fund run by former OpenAI researcher Leopold Aschenbrenner, rode a concentrated, leveraged bet on AI infrastructure to a reported net return of more than 400% through June, one of the best runs anywhere.

When making bold predictions, fortunes can change quickly. In late July, when AI stocks sold off, the same concentration and leverage forced the fund to sell its entire public equity portfolio , virtually overnight, to meet margin calls. Same fund. Same thesis. Same structure, six weeks apart.

Michael Raynor called this the strategy paradox : the strategies that produce spectacular success are structurally identical to the strategies that produce spectacular failure. The difference is which future shows up.

The Capabilities-Based Portfolio

A portfolio built for a range of outcomes, taking the capabilities-based approach, makes the opposite trade. It gives up the spectacular right answer to take ruin off the table. The question changes from "what will happen?" to "what could happen, and can I survive the versions I didn't predict?"

Diversification becomes what optionality is to the military planner: paying something today for the ability to respond to many different threats. And sizing follows the same logic: no position so large that being wrong about it is fatal.

None of this argues against having views. The Pentagon didn't stop analyzing threats after 2001; it analyzes more of them, harder. What changed is no single view drives the positioning of the entire institution. It’s the marriage of conviction and humility.

Plan For The Futures You Can’t See

You are a decision-maker under uncertainty. So is everyone with money that has to last longer than the next forecast. Nobody knows the future in advance. I’m not sure what 2036 will look like. I'm sure it will be very little like we expect. Plan accordingly.