Using 5 Whys Properly

5 Whys asks "why did that happen?" repeatedly, following a causal chain from the visible problem back toward something worth fixing. Five is a guide, not a rule — some chains terminate at three, others run to eight.

A worked example

• Problem: A pump seal failed and released product.
• Why? The seal ran dry.
• Why? The flush line was blocked.
• Why? The strainer had not been cleaned for eight months.
• Why? The maintenance task was deferred repeatedly as low priority.
• Why? The task was not flagged as safety critical, so it was not protected from deferral.

The last answer is actionable and would prevent a class of events, not just this one. Stopping at "the strainer was dirty" produces "clean the strainer", which changes nothing about the next one.

Rules for a valid chain

• Every link must be supported by evidence, not by plausibility.
• Each answer must genuinely cause the one above, not merely be associated with it.
• Test each link backwards: "therefore". Read the chain downward and it should make sense as "because X, therefore Y".
• Stop when you reach something the organisation can change, and going further would only produce generalities.