Why, Oh Why? The Importance of 5-Why
Kids understand the importance of asking why. In fact, they've perfected it to an art form. If you've ever spent a few hours with a five-year-old, you've experienced this phenomenon: "Why are we stopping?" "To get gas." "Why do we need gas?" "So the car doesn't stop." "Why will the car stop?" This question and answer process continues, and the next thing you know, you're explaining internal combustion. Invariably, this conversation ends with "Just because," which is the indicator that you've either reached the end of your knowledge on the subject or the end of your patience. The real question is: Why do we stop asking why?

Asking why is an integral tool in the Lean problem-solving process. It's typically referred to as the "5 Why's" or "5 Why's of Root Cause Analysis." Before we go any further, the number five is a bit arbitrary, but it's a pretty good indicator of the average number of steps you need to take in the problem-solving process to get to the heart and real cause of the problem. Continuing to ask why forces a solution to be found upstream from the initial symptom. You might reach the real source of the problem in three steps or ten. It's important to keep asking why until you get there.

Here's a familiar scenario: You find lubricant on the floor, and leakage is an abnormal state. Now you have two choices – clean it up or ask why. Why is there lubricant on the floor? (Okay, you're going to have to clean it up regardless.) It leaked from the machine. Why is the machine leaking? Because the seal is damaged. Again, you can simply replace the seal or ask why again. Why is the seal damaged? Because there are metal shavings in the lubricant. Why are there metal shavings in the lubricant? Because the filter on the lubricant pump is damaged. Why is the filter damaged? Because it gets damaged by contaminants falling into the machine. Ah, now we're getting somewhere.

If we stopped sooner in the process, the problem would have recurred causing continuing waste – the ongoing replacement of seals and filters. Once you discover the root cause (the contaminants), you can take action needed to alleviate all of the other symptoms. The real problem is falling contaminants; the symptoms are the damaged filter, leaky seals and lubricant on the floor. Figure out how to prevent the contaminants, and you've fixed the whole problem.

Some Lean practitioners avoid the 5-Why approach because it's not an objectively repeatable process and is not based on data. Different people may arrive at different solutions, or the same supervisor may arrive at a different conclusion on a different day. (In the example, you may conclude that the contaminants were in the lubricant when it was originally delivered, and that your vendor has a quality control issue.) However, it's an excellent approach to simple problems, or it can be the right first step in tackling more complicated problems.

Another benefit of the 5 Why's approach is that it's easy to teach and easy to learn. Both managers and employees are more likely to use this process because it's easy. As a starter tool, it introduces structured thinking which is the foundation of Lean and quality improvement. When employing the 5-Why process, you and your employees will prevent the Band-Aid approach to problem solving, which typically never really solves a thing.

With 5-Why, you're guaranteed to develop a better solution for any problem as long as your last answer is never "Just because."

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Fishbone Diagrams
The fishbone diagram is a useful tool for determining cause and effect and diagraming the 5-Why process. Also known as Ishikawa diagrams (named for its creator) or herringbone diagrams, they typically include universal categories that contribute to problems:

Equipment: Any machines, computers (hardware or software) or tools needed to complete the process.

Materials: Any raw materials that are needed to complete the process. Input data can be considered a raw material.

Environment: Physical surroundings in which the process occurs that include temperature, humidity, air quality, culture.

Process: How the task is completed. Process factors include specific requirements including policies, procedures, rules, regulations and laws.

People: Anyone who has a role in carrying out the process.

Management: Supervisors and upper management personnel who are responsible for setting policies and approving budgets and expenditures.


The six capstones, or main fish bones, are the main groupings of potential causes. (Some variations substitute "Cause 1, Cause 2" etc. as the capstones.) The detail of each cause is noted on the minor fish bones.

When constructing your fishbone chart, it's helpful to get as many people involved in identifying causes as feasible. Diversity can often provide a quicker solution. It also provides a sense of ownership of the problem, and ownership ignites the solution-finding fire. Also, keep in mind that creating a fishbone diagram is really a brainstorming exercise. Make note of all the ideas regarding contributing causes.

Finally, when the chart is complete, test its logic. The problem happens because of this, this happens because of F, F happens because of E, E happens because of D, D happens because of C, C happens because of B, and B happens because of A. You should be able to track the problem back through each of the major and minor fish bones. Don't skip the logic test. In the heat of brainstorming, it's easy to get a bit off track and possibly created a logic misstep. Without testing, you may end up chasing the wrong solution.
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