How to run a good 5 Whys
- Start with a specific problem statement. "Pump failed" is too vague. "P-12 tripped on high motor temperature at 02:40, line 3 down 3.5 hours" gives the team something to test answers against.
- Answer with facts you can verify. Each answer should be backed by something — an inspection, a reading, a work order history. Record it in the evidence field. A plausible guess that nobody checked can send the whole analysis the wrong way.
- Go past the physical cause. The first couple of whys usually reach the failed part. Keep going until you reach the process or system that let it happen — that's where a countermeasure prevents recurrence instead of just fixing this one.
- Check the chain backwards. Read from the root cause up, saying "and therefore" between each step. If any step doesn't follow, the chain has a gap.
Common mistakes
- Stopping at "human error." People make mistakes in every system. The useful question is why the system made the mistake easy or didn't catch it — unclear procedure, no checklist, missing training, poor labeling.
- Forcing exactly five. Some problems reach a fixable root cause in three; some take seven. The number is a reminder to keep digging, not a rule.
- Following only one path. Many failures have more than one contributing cause. If a "why" has two true answers, run a second 5 Whys for the other branch.
- Countermeasures that only fix this occurrence. "Replaced the bearing" restores the equipment. "Added the bearing to the lubrication route and corrected the grease interval" prevents the next one.
When 5 Whys isn't enough
5 Whys works best for single-path problems with a small team that knows the equipment. For failures with several interacting causes, a fishbone (Ishikawa) diagram helps brainstorm across categories first. For high-consequence events — safety incidents, major outages — use a formal RCA method with a trained facilitator. And to get ahead of failures instead of reacting to them, an FMEA ranks what could fail before it does.
FAQ
Where is my work saved?
Only in this browser on this device. Nothing is sent to a server. Clearing your browser data, or using a private window, will lose the draft — print or copy it when you're done.
How do I get a PDF?
Click "Print / save as PDF" and choose "Save as PDF" as the printer. You'll get a one-page report with the problem, the full chain of whys with evidence, the root cause, and the countermeasure table.
Who invented the 5 Whys?
The technique is credited to Sakichi Toyoda and was built into the Toyota Production System, where it became a core problem-solving habit. It's now used across manufacturing, maintenance, healthcare, and software.
Sources & standards
- Ohno, Taiichi. Toyota Production System: Beyond Large-Scale Production. Productivity Press, 1988. — Describes the 5 Whys as practiced at Toyota.
The “how to” and “common mistakes” guidance is standard practitioner advice from maintenance and reliability work, not a published standard.