pre-mortem

/pre-mortem — assume it failed, work backward

Imagine this has already failed. What went wrong?

The pre-mortem inverts the usual optimistic framing. Instead of asking "will this work?" (which biases toward yes), assume it already failed and work backward to figure out why. Surfaces risks that optimism would hide.

Process

1. Set the scene

State what's being evaluated, what success looks like, the timeline, and the blast radius.

2. Imagine failure

Assume it's 3 months later and this failed. Generate failure scenarios across these categories — they're prompts, not a checklist.

• Mechanism — what breaks under load, scale, or real-world data? Dependency changes? Network slow, disk full, API rate-limits?
• Structure — where does the design leak? What requirements emerge that this can't accommodate? Where is it optimized for today and fragile against tomorrow?
• Boundary — what happens at edges with other systems? Upstream contract changes? Data format evolves?
• Human — what if the next developer misunderstands the design? What if someone uses it in a way you didn't anticipate? Will error messages actually help?
• Operations — how do you know this is working in production? What's observable? What happens when it fails silently? How do you roll back?

After scanning these 5, ask: what doesn't fit any of these that I should worry about? Name it as a 6th. The most dangerous failures are often the ones that don't fit the boxes.

3. Rank by danger

For each failure mode, assess:

• Likelihood — how probable? (not "could it happen" but "will it happen given enough time")
• Impact — recoverable annoyance or catastrophic data loss?
• Detectability — would you know it happened? Silent failures are worse than loud ones.

The most dangerous failures are likely + high-impact + hard to detect. Lead with those.

4. Identify detection strategies

For each significant failure mode: how would you know if it happened? What metric, log line, user behavior, or test would reveal it?

If you can't answer "how would I know?" for a failure mode, that's the most important finding of the whole pre-mortem.

5. Present findings

Don't soft-pedal. The value of a pre-mortem is uncomfortable honesty before commitment, not reassurance.

For each significant failure mode:

• What fails — specific mechanism, not vague hand-waving.
• Why dangerous — likelihood × impact × detectability.
• How you'd detect it — concrete signal.
• What to do — mitigate now, accept the risk, or redesign.

End with a clear recommendation: proceed as-is, proceed with mitigations, or reconsider the approach.

Common pitfalls

• Listing risks you've already mitigated. That's not a pre-mortem, that's a victory lap. Focus on what's still exposed.
• "Everything could fail." Too vague. Name the specific mechanism.
• Only considering technical failures. Human and operational failures are often more likely.
• Treating it as a formality. If every pre-mortem ends with "proceed as planned," you're not being honest enough.
• Dramatic register. State failure modes in neutral, factual language. "Catastrophic" / "disaster" / "irrecoverable" are reserved for actually catastrophic outcomes. Drama sways downstream decisions out of proportion to the actual risk — a recoverable issue framed as apocalyptic gets treated as one.