Making decisions with uncertainty means identifying the assumptions a decision rests on and testing whether you have sufficient certainty to act.
Captain Chesley Sullenberger had 208 seconds between the moment geese destroyed both engines of US Airways Flight 1549 and the moment he landed on the Hudson River. All 155 aboard survived. The NTSB investigation confirmed what was obvious to anyone watching: Sullenberger did not have all the facts. He could not know whether the engines could be restarted. He could not know whether he could reach an airport. What he did was what every proficient Decider does: he identified the decision, tested his options against the assumptions they rested on, and acted. At 200 feet above the water, he still asked his co-pilot, "Got any ideas?" The reply: "Actually, no." That exchange was the final assumption check. There is no option we have missed.
The 208-second version and the six-month boardroom version use the same method. The difference is proficiency, not process. What changes under a short clock is not the method but the preparation it demands, which is why decision making under pressure has to be built before the pressure arrives.
The question people ask me most often is some version of "how do I decide when I don't have all the facts?" I have spent nearly fifty years in advisory practice, and my answer has been the same every time: you are asking the wrong question. You never have all the facts. You never will. Every decision is made under uncertainty. The real question is different, and until you learn to ask it, no quantity of data, consultants, or committee papers will help you.
Why Making Decisions with Uncertainty Feels Impossible
Every decision rests on a mix of facts and assumptions. The distinction matters less than people think, because facts decay into assumptions over time. Setting the price of a new product treats production costs as fact. But production costs change between the decision and its outcomes. Today's fact is tomorrow's assumption.
What matters is not whether you have all the facts. What matters is whether you know which assumptions your decision depends on, how confident you are in each one, and how much influence each has on the outcome you want.
Roger Estall and I developed the Universal Decision-Making Method over decades of work across mining, finance, aviation, and public health. The single most valuable question we found, across every context, was this: "What are the assumptions we are making here?"
That question does more work than any risk register, any Monte Carlo simulation, any scenario-planning exercise. It forces the invisible into the open.
Sufficient certainty, not maximum certainty
The method does not ask Deciders to eliminate uncertainty. It asks them to reach sufficient certainty that the desired outcome will be achieved.
Sufficient certainty means the Decider has surfaced the assumptions, assessed their significance, addressed the critical ones, and judged that what remains is acceptable. The distinction from maximum certainty is not semantic. Chasing maximum certainty has a price, and sometimes that price is catastrophic.
That judgement belongs to the Decider. No formula produces it. No consultant delivers it. As we wrote in Deciding: "There is no valid formulaic approach that can be used universally to calculate sufficiency. What is sufficient for one Decider might not be sufficient for another."
How to assess which assumptions matter
Not all assumptions carry equal weight. The method classifies each assumption on two dimensions: its influence on the desired outcome, and the Decider's confidence that it will hold. These two dimensions produce four zones of significance, from Critical down to Limited.
Critical assumptions have high influence and low confidence. They are the ones that will ruin the decision if they break. Limited assumptions have low influence and high confidence and can be noted and set aside. The value of this classification is not in the matrix itself but in the conversation it forces. When a team sits down and asks "how confident are we that this assumption will hold for the life of this decision?", the quality of the decision improves before anyone has taken a single action.
This is step three of five in the method. Surface the assumptions. Classify their significance. Address the critical ones before proceeding. If you cannot reach sufficient certainty after addressing them, adjust the decision and iterate. Making decisions with uncertainty is not a one-pass exercise. It is an iterative loop between tentative decisions and assumption testing.
Why more data does not solve the problem
The 2007 Global Financial Crisis demonstrated what happens when Deciders treat models as the decision itself, mistaking deep uncertainty for calculable risk. Ratings agencies and investment banks had sophisticated quantitative models for assessing credit risk. Those models assumed a benign, stable economic environment. When the environment changed, the models continued to produce reassuring numbers. Deciders continued to rely on them. The models were not wrong in their mathematics. They were wrong in their assumptions.
The Queensland Floods Commission of Inquiry told a similar story. Operators at Wivenhoe Dam had real-time inflow data and a rule-based manual. The manual's assumptions no longer held. The subsequent flood caused billions in damage. Boeing's 737 MAX certification relied on a flight control system fed by a single angle-of-attack sensor. The House Committee investigation found the same pattern: assumptions that were never surfaced or challenged. 346 people died. A decision autopsy would have required a single question: what are we assuming, and how confident are we?
Enron maintained one of the most elaborate risk-management structures in corporate America. The Australian banking sector passed regulatory reviews for years before a Royal Commission exposed systemic misconduct. In every case, extensive analytical machinery created the illusion due diligence had been done.
Accumulating more data without surfacing the assumptions that data rests on is not making decisions with uncertainty. It is theatre.
What to do instead of waiting for all the facts
If you are facing a difficult business decision and feel paralysed by incomplete information, start with Purpose: not the goal of this decision but the broader Purpose it serves. Name your assumptions and write them down, because every assumption you leave unstated is an elephant in the room. Classify each assumption by influence and confidence, and give your attention to the Critical ones. Build monitoring into the decision before you finalise it: specify what you will watch, who will watch it, and what triggers a revision. Then decide.
Sufficient certainty is the target. Not maximum certainty. Not "one more report." You have enough when you have surfaced the assumptions that matter most and addressed them honestly. That is what decision making under uncertainty actually looks like.
Grant Purdy is the co-author, with Roger Estall, of Deciding (2020), and the architect of the Universal Decision-Making Method.
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