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When something goes wrong, especially in a large organization, there can be an instinct to point fingers and shift blame. This probably isn’t the best way to prevent the problem from arising in the future though. Sakichi Toyoda, the founder of Toyota Motor Company, developed the “5 Whys” process, a type of root cause analysis, to identify and fix problems that arose within the company. It has since been widely adopted as part of lean manufacturing, Kaizen, and Six Sigma methodology.
Anyone who has ever been around a three-year-old will immediately recognize the basics of a 5 Whys inquiry. As the name implies, the main work of the analysis is to keep asking “why?” until the root cause of a problem is reached. There is no rule that you must stop at five, but usually within five repetitions is enough.
Before you can ask why a problem occurred, it is necessary to articulate what the problem is. The problem should be as specific as possible without oversimplifying it. This specificity helps to ensure that everyone can agree upon what the problem actually is and avoid blind men and the elephant situations.
Beyond just agreeing on what the problem is, everyone involved should understand, at least at a basic level, what the problem is. If the formulation of the problem is too technical, the inquiry may not include everyone at the table. If it is too vague or broad, inquiry will become muddled and unproductive.
Once the problem has been articulated, the interrogation begins. As the name implies, this is the heart of the inquiry. Starting with the problem, ask why it occurred. The problem is an effect, try to articulate the cause of it.
It is essential that this process be taken slowly. Jumping to conclusions invites error and risks conflating symptoms and causes. When complete, each connection will be logically sound and the root cause can be traced to the problem by a series of “and therefore” statements.
It is necessary that each “why?” be answered with a cause that is both necessary and sufficient to cause the previous step. “Necessary” means that if not for the cause, the effect would not happen. “Sufficient” means that the cause is enough to make the effect happen on its own. If there is no singular sufficient cause, it might be necessary to pursue two parallel lines of inquiry or consider using a different troubleshooting method.
After five (or so) iterations of “why?” a root cause should be reached. If the analysis has been properly conducted, elimination of this root cause will prevent the error in future. This can be checked by starting with the root cause and working back up the chain of causation.
The root cause should always point to process. This is an essential, but often overlooked aspect of the 5 Whys method. A common adage in this vein is: "people don’t fail, processes do". Similarly, it is not useful to point to root causes that are out of our control, like blaming the problem on a tornado. Processes are within our control. If the cause reached can’t be changed or isn’t a process, keep asking why until a viable root cause is identified. In the tornado example, the next answer to “why?” might be, “Our emergency and contingency procedures did not sufficiently address natural disasters.”
The investigation ends by formulating and deploying countermeasures. These should be distinguished from simple “solutions”. A solution fixes this instance of the problem, but is only a treatment, not a cure. Countermeasures are more robust, and consist of a set of actions aimed at preventing the root cause from occurring again.
If the planned counter measure is not feasible, ask “why?”. It could be that you haven’t really identified a root cause that is under your control. If the countermeasures are more expensive or time consuming than treating the problem, try redesigning it. Countermeasures should make as few changes as possible, while still eliminating the root cause.
The 5 Whys comes out of Toyota’s philosophy of Genchi Genbutsu (現地現物), often translated as “go and see”. This is because, unlike some other root cause analyses, the 5 Whys is meant to originate with the people closest to the process. It doesn’t require special skills, or statistical training, just a familiarity with the process under consideration. Even lay people can perform the analysis, with a little help from experts or reference materials.
It is vital that the people asking “why?” be the people who know the system that is broken. If the people conducting the inquiry aren’t familiar with the process, they won’t be able to construct a robust causal chain. This doesn’t mean that management should be excluded from a 5 Whys inquiry; they need to understand what went wrong, and are important stakeholders in the design and deployment of countermeasures. However, management should step back and allow domain experts to lead the analysis.
Tracing problems back to their root cause is an inherently narrative process. Each event in the chain of causation is linked, and should create a coherent narrative. Storyboards serve this effort as thinking aids, but also for communicating to stakeholders what went wrong and how it will be fixed. Because the root cause is always a process, and countermeasures should be designed to improve that process, the results of a rigorous 5 Whys inquiry will be a narrative of how the problem will never happen again.
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