Library skill · Thinkers' principles

Ohno-style 5 whys root-cause analysis

v1.0.1 · Updated 4 November 2026

Finds the root cause of a problem with the 5 whys Taiichi Ohno illustrated: a measured gap, a chain of whys with evidence at each step, and a fix for the cause, not the symptom. Use it when an incident, defect or missed delivery needs a root cause.

Not affiliated with or endorsed by Taiichi Ohno or their companies. About these principles: Taiichi Ohno's ideas, explained.

Works in Claude, ChatGPT, and coding agents. On Team and Business, this library skill in your pod updates itself when we improve it.

When to use it

• An incident, defect or missed delivery needs a root cause
• The same problem keeps coming back after it was fixed

What you give it

• The problem and the standard it missed
• Logs, timelines and records
• What has been tried
• Who can confirm missing facts

What you get

A why-chain table with evidence per step, a read-back check, the root cause, containment and root-cause countermeasures with owners, and how you'll know it worked.

How it works

1. State the problem as a gap "Orders shipped late: 12 of 140 last week, against a standard of same-day dispatch before 15:00." Specific, measured, with the standard (principle 4).
2. Ask the first why Why did the gap happen? Write the direct, observable cause, with its evidence.
3. Keep asking (principle 1) Take each answer and ask why it happened. One line per step, each with its evidence. If an answer has two causes, branch and follow both.
4. Check each link Read the chain backwards with "therefore": "No strainer, therefore metal got in, therefore the shaft wore ...". If a "therefore" doesn't hold, the chain is wrong at that step.
5. Stop at the root (principle 2) Stop when the next why leaves your control (the weather, the law) or when the cause found is one you can remove and that would stop the failure. That may be after three whys or seven.
6. Set countermeasures (principle 3) One for the root cause (the strainer), and, if needed, one for containment now (replace the fuse). Label them; containment alone is not a fix.
7. Name an owner, a date and a check How will you know in two weeks that the problem doesn't recur?

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Changelog

• v1.0.1 · 4 November 2026 · Example output now opens with the attribution and not-affiliated lines, as the skill's own checks require.
• v1.0.0 · 4 November 2026 · First release.