Five Whys

Applications

Discovering the root cause of a problem or defect. Since there may be more than one root cause, the method has to be repeated asking a different sequence of questions for every supposed cause. Its purpose is to determine the actual root cause of an issue or problem so that it can be addressed. In essence, you simply keep asking "Why?" every time you discover a contributing cause and the theory is that after 5 rounds you will have reached or be near to reaching the root cause.

Not all problems have a single root cause. If one wishes to uncover multiple root causes, the method must be repeated asking a different sequence of questions each time.

The process has to be disciplined so that the team will push itself to reach a root cause and not stop once a reason for a defect is identified. This method is related to the Cause & Effect or the Fishbone diagram, and can be used to complement the analysis necessary to complete a Cause & Effect diagram

Benjamin Franklin's 5-Why Analysis:

1. For want of a nail a shoe was lost,
2. for want of a shoe a horse was lost,
3. for want of a horse a rider was lost,
4. for want of a rider an army was lost,
5. for want of an army a battle was lost,
6. for want of a battle the war was lost,
7. for want of the war the kingdom was lost,
8. and all for the want of a little horseshoe nail.

Example

Procedures

Determining the root cause of a problem by repeating the question "Why"?. Each subsequent answer forms the basis for next question.

Instructions

An example of the process follows^[1]:

The vehicle will not start. (the problem and the source for the first why)

1. Why the vehicle doesn't start? - The battery is dead. (the answer will be converted in the second why)
2. Why the battery is dead? - The alternator is not functioning. (converted in the third why)
3. Why the alternator doesn't work? - The alternator belt has broken. (converted in the fourth why)
4. Why the alternator belt is broken? - The alternator belt was well beyond its useful service life and not replaced. (converted in the fifth why)
5. Why the alternator belt was not replaced at the end of service life? - The vehicle was not maintained according to the recommended service schedule. ( the answer is the root cause)

Notes