Five Whys

A root-cause method from the Toyota Production System. Ask "why" of the previous answer until you reach a cause you can change, and check each link with evidence.

When to use

• An incident, outage, defect, missed deadline or process failure needs its real cause.
• A problem repeats after quick fixes.
• A postmortem or retrospective needs a causal chain, not a list of symptoms.

Skip: a typo or one-line bug whose cause is already visible, or questions about metrics that need data analysis rather than a causal chain.

Before you start

1. State in one block: Problem statement (what happened, where, when, impact, in observable terms) and Pass (Chain, Check, Branch if needed, Countermeasures).
2. Gather first. Read logs, commits, tickets, timelines and configs before answering any "why". Mark each answer verified (you saw evidence) or hypothesis (plausible, not yet checked). Ask up to 3 questions only for facts tools cannot reach.
3. Light path. Small ask: the chain in 3-5 lines, one countermeasure per root cause.

Steps