Five whys
Five Whys is a root-cause-analysis technique: ask 'why?' five times in a row (or until the answer becomes systemic rather than situational) to find the underlying cause of a problem. Popularised by Toyota in the 1950s, it's the most-cited technique in incident postmortems and process retrospectives.
Example: the deploy failed (1: why?) because the migration timed out (2: why?) because the table lock blocked other writes (3: why?) because the migration didn't use a non-blocking variant (4: why?) because the team's runbook didn't flag online migrations as a separate path (5: why?) because no one had hit this case before. The fifth 'why' usually exposes the systemic gap — in this case, runbook coverage. Five is a guideline, not a rule: stop when the answer is something the team can actually act on.
Related terms
- Postmortem
A postmortem is a structured retrospective on an incident or failure — capturing what happened, why, what was learned, and what will change.
- MTTR
Mean Time To Recovery is the average elapsed time between an incident's detection and its resolution.
- Technical debt
Technical debt is the accumulated cost of shortcuts taken during development — code that's harder to change than it should be, missing tests, outdated dependencies, or architectural choices that no longer fit.