5 Whys is a commonly used, simple and logic quality tool to dig down into a problem, identifying its causes and cause-effect relationships. The technique itself was developed by Sakichi Toyoda, founder of the Toyota Industries (the present Toyota Group). He found out that asking five questions in a logic sequence can be efficient to recognize the real cause(s) of a problem.

Instead of having symptomatic treatment, the aim of 5 Whys (or also referred to as 5W or "Five times why") is to identify the real cause, and having it erased, the problem will not occur again.

During a 5W analysis, we go through the logic chain, analysing the sequential causes of the problem. Every 5W starts with a precise problem statement. After understanding the problem, we start to ask why the problem occurred, and we answer it with proof. Generally, the answer will be the base of the next question, and so on, repeating the question-answer link step by step, until we dig deep enough to our final cause conclusion, however we may only be certain that we found the root cause if it is proven with evidences.

Making a cross-check is advisable by going through the whole logic chain (sequence) with the reverse "therefore" systematic.

A 5Whys example for a simple case:

In case we receive a claim from our customer, it means the failure not only did happen, but also slipped through, as we didn’t recognize it in our organization. Besides searching for the causes of failure occurrence (non-conformance), we have to identify the causes of non-detection. 5 Whys is also usable for identifying the cause of non-detection.

Depending on the characteristics of the problem, it may have various, coefficient root causes that are simultaneously necessary to set off the failure. In such a case, we can build a cause-effect tree (Why tree) with separate failure paths, also called Fault Tree Analysis (FTA) in quality management.

Benefits of technique:

5 Whys is an independent element of root cause analysis, however it can be linked to other techniques, such as Ishikawa (also called fish-bone or cause-effect diagram). In such case we can:

Five is just a rule of thumb, there are problems that are more complex, resulting a deeper logic chain, with 7-10 levels, or even more.

Once the problem is stated, it is a general and usual mistake that the team jumps over the next logic step (why) during the cause-sequence elaboration. This leads to the misunderstanding of the real rot cause. In deep technical or organizational issues, the answers are not as trivial as they seem to be.

It is imperative to go down to the deepest roots of the cause, otherwise there is a high chance we only see the top of the iceberg, thus we will only eliminate the top causes. Doing so, the problem will probably reoccur sooner or later. To find the deepest causes, we distinguish technical and management root causes, which is essential in efficient Problem Solving.