Five Whys


Five Whys is used to explore cause-and-effect relationships and to unearth underlying processes that are the root causes of a particular problem.

Also known as

The tool

The tool is used to identify the root cause of a problem by repeating the question Why? over and over.

The purpose of the tool is to encourage users to avoid making assumptions and instead trace the chain of causality from the effect (problem) to one or more root cause(s), while showing the connection from the cause to the problem.

The root cause should point toward a process that is not working well or does not exist.

The answer to each ‘Why?’ question informs the next. The 5 in the name is not prescriptive, but indicates the likely number of questions that will have to be asked before a root cause is identified.

Not all problems have a single root cause. Where users wish to identify multiple root causes, then separate sets of questions will have to be asked for each individual cause.

The method is flexible, and does not prescribe hard and fast rules about lines of questioning or how long users should continue to look for additional root causes.

Why use it

When to use it

How to use it


  • Flexible, and therefore can be used in a wide range of situations.
  • Simple to understand.


  • Users will stop at identifying symptoms, rather than continuing to find root causes.
  • Users may not ask the right ‘why’ questions.
  • Results cannot be replicated – different people identify different causes for the same problem.
  • There is a tendency for users to stop at the identification of a single root cause, although there may be several or many.
  • Users cannot find causes that they do not already know about.

Use in conjunction with

Complemented by


Additional information