Thinking models in practice: the pre-mortem

A pre-mortem is a planning exercise in which you assume the project has already failed — it is a year from now and it went badly — and list the reasons why. Because the failure is treated as a fact rather than a possibility, people name risks they would otherwise keep to themselves. It takes about twenty minutes and works best right before a decision is final.

This is the first post in a short series, Thinking models in practice: one classic method per post, what it is for, how to run it by hand, and how to run it on your own material.

Where it comes from

The psychologist Gary Klein popularised the pre-mortem in a short Harvard Business Review piece in 2007. It rests on an older finding about "prospective hindsight": imagining that an event has happened makes it easier to generate explanations for it than imagining that it might happen. "Why might this fail?" invites reassurance. "It failed — why?" invites a story.

When to use it

• A plan is about to be approved and everyone is quietly enthusiastic.
• You are the person who proposed it, and you know you are not the right one to find its flaws.
• The failure would be expensive and slow to notice: a launch, a hire, a migration, a move.

It is less useful early, when the plan is still vague. You cannot imagine the failure of something that has no shape yet.

How to run it

1. State the plan in one sentence, with a date. "We launch the paid tier to existing users on 1 March."
2. Declare the failure. "It is a year later. The paid tier was a disaster." No hedging.
3. Everyone writes reasons silently, for a few minutes, before anyone speaks. This step is the method; discussion first means the most senior voice sets the list.
4. Go round, one reason each, until the reasons run out. Write them all down. No rebuttals yet.
5. Pick the two or three that are both plausible and serious, and decide what would change in the plan because of them — a check, a trigger, a smaller first step.

Alone, you can run steps 2–5 on paper. The silent-writing step matters even more: your first reason will be the one you were already worried about, and the useful ones come after it.

A worked example

Plan: an open-source project with no marketing budget aims to reach its first 100 active users in three months by posting on two developer forums.

It failed. Why?

• The posts landed, but the install took forty minutes on a clean machine, and most people gave up.
• "Users" was never defined, so the team celebrated 400 stars while active use stayed in single digits.
• The one forum that worked attracted people with a different problem; their feature requests pulled the roadmap sideways.
• The maintainer burned out answering support questions in week three.

The changes: define an active user before launch, record a clean install from scratch, and pick one narrow audience instead of two broad ones.

Running it with AI

AI is good at the part people find hardest — generating many specific failure stories quickly — and bad at knowing which ones matter for you. Two rules keep it useful:

• Give it the real plan and the real context, not a topic. "A launch" gets generic risks. Your plan document, your numbers and your constraints get specific ones.
• Keep the selection step human. The AI produces candidates; deciding which two to act on is yours.

In MindMax, the pre-mortem is in the canvas's starter library — install it once, then apply it to a card holding your plan, with the planning documents attached. Each failure story comes back as its own branch, which you can expand, drop, or turn into a check. The built-in red team is a close cousin: instead of "it failed, why?", it attacks the plan from an adversary's side.

The red team, a built-in cousin of the pre-mortem, run on one card of a launch plan.

Where it goes wrong

• It becomes a list of everything. Twenty risks with no selection is anxiety, not planning. End with two or three changes.
• The plan is too vague. "Grow the business" fails for every reason at once.
• Nobody acts on it. A pre-mortem that changes nothing in the plan was a meeting.

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More methods like this: thinking models on the canvas, and the definition in the glossary: mental model. Next in the series: the steelman.