# 5 Whys

Operations · `5 Whys` · verification: source checked

5 Whys is a root-cause analysis method that repeatedly asks why a problem occurred. It continues past obvious symptoms until the underlying cause is reached, so countermeasures can prevent recurrence.

## Specification

| Property | Value |
|---|---|
| Kind | methodology |

## Study notes

- The specific number five is not the point; keep asking why until the root cause is reached and eliminated.
- 5 Whys is used with Gap from Standard problems, focusing on specific problem definition, goal setting, root cause analysis, countermeasure establishment, and checks, standards, and follow-up activities.
- Root-cause analysis types listed are logic, one-variable-at-a-time (OVAT), and multivariate-at-a-time (MVAT).
- Logic-based analysis such as 5 Whys requires no advanced math skills but requires critical thinking using inductive, deductive, and abductive logic.
- Taiichi Ohno's example traces a machine stop from a blown fuse to an overload, insufficient lubrication, a lubrication pump issue, a worn pump shaft, and no strainer allowing metal scraps to enter.
- Also called Five Whys.

## Sources

1. [5 Whys - What is it? | Lean Enterprise Institute](https://www.lean.org/lexicon-terms/5-whys/) (accessed 2026-10-25)

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