The 5 Whys

Root Cause Analysis

By Nathanael Okhuysen

“‘For want of a nail’ the kingdom was lost.”

Sakichi Toyoda’s 5 Whys

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.

Steps of a 5 Whys Analysis

5 Whys Overview
Create your own at Storyboard That Articulate the Problem Construct a Causal Chain Identify the Root Cause Deploy Countermeasures • Specific and clear • Agreed upon • Understood by everyone • Keep asking: "Why did this effect occur?" • Causes must be necessary and sufficient for effects • Generally, 5 times is enough • Without this cause, there would be no problem • This cause alone caused the problem • A fixable process, not a person • Addresse the root cause, not symptoms • Prevent the problem from ever occurring again • No more complicated or expensive than necessary Royal Horseshoe Inspection Checklist


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Articulate the Problem

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.

Create a Causal Chain

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.

Necessary and Sufficient Conditions
Create your own at Storyboard That Neither Necessary, nor Sufficient Sufficient, but not Necessary Necessary, but not Sufficient Necessary and Sufficient Being human means you can talk. (Some birds can speak, and some humans cannot) The sidewalk is wet because it's raining. (The sidewalk could get wet from some other cause, a hose, for instance.) You have to be 30 years old to serve as a US Senator. (Being 30 is not enough to make you a senator though.) Lighting causes thunder. (Thunder cannot be caused by anything other than lightning.) Causation