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Investigate a cause

5 Whys

Investigate a specific event through successive causal questions, keeping each explanation tied to evidence.

When to use it

Start with an observable incident when you have records or direct observations to investigate. Use an issue tree first if the problem has several distinct investigation paths.

What to bring

A bounded problem, the affected cases and time period, and records that can support or challenge each proposed explanation.

What you will have

A causal investigation showing supported links, unresolved hypotheses, and the next evidence to collect.

How to use it

  1. Describe what happened, to whom, and during which period.
  2. Ask why the event occurred and record the evidence for the answer.
  3. Ask why again within the supported scope. If an answer explains only a subset, keep the other cases open.
  4. Stop or branch when needed. Define the observation or check that could confirm or challenge the next explanation.

Keep its limits in mind

Five is not a required number of questions. Stop when evidence runs out, and branch when there are multiple causes. A plausible chain is not proof of a root cause.

Fictional teaching example

Investigating stock confirmation in delayed orders

In this fictional case, 20 of 100 orders missed their promised dispatch date. Stock confirmation was the first recorded blocker for 8 of the late orders. This investigation follows that branch only.

?Problem to investigate8 orders missed dispatch with stock confirmation recorded astheir first blocker.1Why 1Stock had not been confirmed before the cutoff.2Why 26 needed a manual lookup in another stock record; 2remain unexplained.3Why 3For those 6 orders, displayed stock differed fromwarehouse availability.4Why 4To verify: update timing or stock reservations mayexplain the difference.5Why 5Not provided

On a small screen, scroll across the diagram to read it.

Preserve the scope: The six-order explanation does not account for the other two orders in the stock branch, or for the other late orders.

Next check: Compare update timestamps, reserved stock, and warehouse counts before treating either hypothesis as a cause.

Next step: Keep the unexplained orders visible. Do not fill the fifth answer just to complete the diagram.

Check your work

  • Each answer explains the previous question.
  • Facts, assessments, and hypotheses remain distinguishable.
  • The investigation does not turn a subset explanation into a claim about every case.
  • The next step describes evidence to inspect, not simply another opinion to collect.

Method references

Put the method to work

Use this framework in the English Workspace with early access. Local generation copies clearly labeled fields; you can edit the diagram afterwards.

Open in Workspace

Practice with an example

Compare 5 Whys and issue trees using the same late-order evidence, then plan your next investigation.

5 Whys vs issue trees for investigating a problem →