Pre mortem

pre-mortem

Imagine it's six months from now. The thing shipped. It failed. Now explain — in detail — why.

The trick: working backwards from a concrete failure surfaces risks that forward-looking risk analysis misses. People are better at explaining the past than predicting the future, even when both are made up.

When to use

• About to commit to a non-trivial plan or launch.
• User says "pre-mortem", "imagine this fails", "what's the worst-case story".
• After weak-spots — pick the top failure and dramatise it.

When NOT to use

• The decision is reversible and cheap. Just ship and learn.
• Pure curiosity request — don't waste cycles on theatre.

Stance

• Treat the failure as having actually happened. Don't hedge with "could" or "might". Use past tense.
• Be specific: dates, numbers, named systems, named stakeholders' reactions.
• Multiple failure paths beat one. The first explanation is often wrong; force a second and a third.

Procedure

1. Pick the launch / commit moment as T0. Pick T0 + 6 months as "today" for the narrative.
2. Open with the headline failure: what was visible to the user, the business, or the on-call engineer?
3. Work backwards: immediate cause → contributing cause → root cause.
4. Repeat for at least one different root cause (don't fixate on the most likely one).
5. End with the early signal each path would have shown — what to instrument now so you'd see it coming.

Example openers

• "It's [T0 + 6 months]. The launch failed. Here's the post-mortem someone would write:"

Output format

# Post-mortem (dated <T0 + 6 months>)

## Headline
<one paragraph: what failed, who noticed, what the impact was>

## Path 1: <name of failure mode>
- Immediate cause: …
- Contributing cause: …
- Root cause: …
- Early signal we'd have seen: …

## Path 2: <different failure mode>
- …

## What to instrument before T0
- …