Core Idea
Definition
A premortem is a prospective analysis that assumes a future plan failed and asks why, while a postmortem is a retrospective analysis that examines an actual result to understand causes, mistakes, and lessons.
In Plain English
One helps you catch problems before they happen. The other helps you learn honestly after they do.
How It Works
Premortems and postmortems work because human judgment changes with timing. Before action, people are often overconfident and under-imaginative about failure. A premortem grants permission to surface concerns without sounding merely negative. After action, people are tempted to simplify, defend identity, or assign blame. A postmortem creates a structured review of what signals were missed, what assumptions failed, and what should change next time. Used together, the pair closes the loop between foresight and learning. One improves anticipation, the other improves adaptation.
When to Use
- •Before launching a project, strategy, or high-stakes decision
- •After a major success, failure, or surprising outcome
- •When teams need a safer way to discuss risk before committing
- •When repeated mistakes suggest lessons are not being retained
- •When trying to separate process quality from outcome luck
Examples
Everyday
Before a difficult conversation, you imagine it going badly and identify what tone, timing, or assumptions could cause that. Afterward, you reflect on what worked and what you would change next time.
Professional
A team performs a premortem before launch to list likely failure points, then later runs a postmortem to compare predicted risks with what actually happened.
Extreme Case
In high-reliability environments, structured pre-incident and post-incident reviews can be the difference between isolated failure and recurring catastrophe.
Common Mistakes
- •Running a premortem but ignoring the risks it uncovers
- •Treating a postmortem as a search for who failed rather than what failed
- •Focusing only on spectacular errors while ignoring subtle process flaws
- •Reviewing outcomes without checking whether the original decision logic was sound
Limits & Failure Modes
- •A premortem can become performative if no mitigation steps follow
- •A postmortem can collapse into blame instead of learning
- •Too much ritual can make the process feel bureaucratic rather than useful
- •Both methods are weaker when psychological safety is low
How to Practice
assume it failed
Before acting, imagine the plan failed badly and write the most plausible reasons without censoring yourself.
process vs outcome review
After results arrive, separate whether the reasoning was good from whether the outcome happened to be favorable.
lesson to change
For every insight from a premortem or postmortem, define one concrete adjustment to process, assumptions, or safeguards.
Related Cognitive Biases
optimism bias
Premortems counter the tendency to underweight failure before acting.
hindsight bias
Postmortems help prevent the illusion that outcomes were obvious all along.
self serving bias
Structured review reduces the tendency to protect identity instead of extracting lessons.
Related Mental Models
Related Skills
Advanced Notes
Historical Origin
The postmortem has long roots in engineering and medicine, while the premortem was later formalized in psychology and management practice.
Philosophical Context
Together they link prospective and retrospective reasoning, creating a feedback system for judgment and learning.
Further Reading
- Thinking in Bets by Annie Duke
- Decisive by Chip Heath and Dan Heath
- Sources of Power by Gary Klein