ronniepinnell /premortem — It Already Failed. Write the Report.
Prospection is weak; hindsight is strong. The trick is to fake hindsight: declare the failure as an accomplished fact, and the failure modes people couldn't "imagine" become obvious. Ten minutes here routinely deletes the worst week of the next quarter.
Invocation
/premortem the pgvector search migration
/premortem # premortem the plan currently under discussion
Procedure
Set the scene, in past tense, as fact: "It is 3 months from now. shipped. It failed badly enough that we rolled it back / lost the customer / spent a week firefighting."
Write 5–8 causes of death. Each one concrete and past-tense — "the migration locked the events table for 40 minutes at peak", not "performance issues". Force coverage across categories; at least one from each:
- Data — bad/missing/dirty data, volume 100× the test set, migration loss
- Integration — the dependency that behaved differently than its docs
- Human — misuse, misunderstanding, the user who clicked the other button
- Scale/time — worked at demo size, died at real size; the slow leak
- Assumption — the thing everyone "knew" that was false
Score each cause: likelihood (H/M/L) × blast radius (H/M/L).
For every H×H and H×M, do one of exactly three things, now:
- Redesign — change the plan so this death can't happen
- Gate it — hand it to
/gate: metric, threshold, checkpoint, on-fail - Accept it — in writing, with the owner's name on the acceptance Anything else ("we'll be careful") is not a mitigation.
Output block (goes in the plan/PR/issue):
PREMORTEM: <X> deaths: <n> | hardened: <n redesigned + n gated> | accepted: <n, by whom> top risk: <one line> → <what changed because of it>
Rules
- Past tense is mandatory. "Could fail because" reopens the door to optimism; "failed because" keeps it shut.
- If the premortem finds nothing scary, the scene wasn't set hard enough — raise the stakes ("we lost the biggest customer") and rerun once.
- Timebox: 10–20 minutes. A premortem that becomes a design review lost its job.
Composes with
/door— mandatory before walking through any one-way door./gate— step 4's "gate it" outputs land there./refute— after shipping, the top causes of death are the first refutations to run against "it works"./altitude— premortems catch wrong-altitude designs before they ship./think— /premortem isinvertspecialized for shipping; /think covers the open field./verdict— top causes of death and their mitigations are logged there.