The 5 Whys technique was developed by the “King of Japanese Inventors”, Sakichi Toyoda, the founder of Toyota Industries.
Over the years, Toyoda invented a variety of textile industry devices, fueling systems for his machines and the famous power loom for which he implemented the Jidoka (automation with a human touch) principle. He often used the 5 Whys technique, the approach of repeating the question “Why?” several times to understand the cause and effect relationship and get to the root cause of any particular problem.
The 5 Whys approach doesn’t necessarily mean that you should ask “Why?” exactly 5 times. It means that you should ask the question as many times as you need to uncover the real root cause of the problem. Sometimes this could be 3 or 4 times, other times, could be 7-8 iterations and so on.
The 5 Whys technique became very popular in the 50’s and 60’s, as Taiichi Ohno, the father of the Toyota Production System (TPS), was an avid user of this technique. He considered it as central to the TPS and described it as the basis of Toyota’s scientific approach. He also used to emphasize that you should investigate and assess the process, not the people, as human error is not acceptable as a root cause. It is the process and not the people that fail. The process should have controls implemented in place to prevent the human error from occurring.
Identifying the real root cause will help prevent the problem from happening again in the future. Below is the classic example of Toyota’s machine failure. Ohno often used this example to teach his students about the 5 Whys method, how to uncover the root cause, implement corrective actions and put controls in place to prevent reoccurrence:
- Why did the machine stop?
There was an overload, and the fuse blew.
- Why was there an overload?
The bearing was not sufficiently lubricated.
- Why was not lubricated sufficiently?
The lubrication pump was not pumping sufficiently.
- Why was it not pumping sufficiently?
The shaft of the pump was worn and rattling.
- Why was the shaft worn out?
There was no strainer installed, and metal scrap got in.
The 5 Whys can easily uncover the problem when dealing with a particular occurrence in the process or when you encounter special cause variation. However, even though it is simple and easy to use, the 5 Whys technique has its limitations. Sometimes it is more difficult to uncover the real root cause of the problem, especially when you are trying to address common cause variation. In this case, a good approach is the Ishikawa diagram, also known as the Fishbone or cause-and-effect diagram. You can use the Fishbone in conjunction with the 5 Whys, as needed. The focus should always be building the quality in and preventing the problem from happening in the first place.
Here is a simple animation of Ohno’s example from Lean Enterprise Institute: https://www.youtube.com/watch?v=acHG75ZQSMQ&t=111s