5-Why is a simple approach for exploring root causes and instilling a “Fix the root cause, not the symptom,” culture at all levels.

Invented by Japanese Industrialist Sakichi Toyoda, the idea is to keep asking “Why?” until the root cause is arrived at.

The number five is a general guideline for the number of Why’s required to reach the root cause level, but asking “Why?” five times versus three, four, or six times is not a rigid requirement. What matters is that we fix recurring problems by addressing true causes and not symptoms – this is real progress.

The following example shows a 5-Why analysis completed after a customer received an incorrect item.

5-why example for wrong item shipped

The 5-Why thought process guides us to lasting corrective actions because we address root causes and not symptoms. Let’s look at the effects of addressing the 1st “Why?” versus the 5th “Why?” in the above exercise –

5-Why possible solutions

Note the improvement in corrective action effectiveness as each deeper “Why?” is addressed:

  • Responding to the first “Why?” is almost counterproductive: we are retraining the stock pickers in our warehouse because we assumed that they pulled the wrong item from our inventory. In reality, the stock pickers performed their jobs perfectly, and the real cause was mislabeled parts coming from the supplier.
  • Addressing the third “Why?” (having the supplier check their stock for other mislabeled products) is much more effective that addressing the first “Why?”, but this action will have no lasting effect beyond fixing the current inventory situation.
  • Addressing the fifth “Why?” is powerful, because it focuses on the true cause: mistakes being made in the label application process.

World class companies routinely address systemic causes like the 5th “Why?” above, eliminating reactionary problem solving and shifting resources to prevention activities over the long run.

Leading a 5-Why Exercise

1. Schedule the Discussion

Schedule a time for the 5-Why discussion, and invite individuals who know about the product and/or process at hand. Your goal should be to run an efficient meeting and complete the 5-why in one session, no more than an hour long. 5-Why is not meant to be a lengthy exercise.

2. Plan for a Successful Outcome

Clearly state the problem and desired outcome in advance of the meeting, via the meeting notice, email, etc.. An example of this would be: “Complete a 5-Why analysis on problem ABC and understand next steps for further investigation / corrective action.” Have an easel pad or large dry-erase board in the meeting room (or better yet, in the workplace), and have the problem statement and 5 Why column headers already documented before the attendees show up.

3. Run a Successful Meeting

Remember that the success of your meeting will determine attendance at your future meetings! You want to have a reputation for holding productive meetings, being highly respectful of attendees while keeping the meeting on track to achieve desired outcomes.

Take a couple of minutes at the start of the meeting and explain that 5-Why is a way to document root causes, showing an example (use the Powerpoint file above if you don’t have a more relevant example from your company).

Take another couple of minutes to clearly state the problem, and make sure everyone agrees with the problem statement. The more specific the problem statement, the better.

4. Agree on Follow-Up Actions / Next Steps

Take the time necessary to document those actions/next steps with the team, and then follow up to ensure those actions are implemented.


5-Why is useful for straightforward problems with systemic causes, as in the case noted above. In cases where the root cause is not readily apparent, 5-Why by itself will likely not solve the problem.

For example, if a toy manufacturer want to improve the color consistency in a given product, they will need to understand which factors influence color the most (otherwise they might not need a Six Sigma project to begin with). In cases like this, structured analysis methods like multi-vari, correlation analysis, and DOE may be necessary to actually learn the physical relationships between the input variables (process settings, raw materials, etc.) and output variables (in this case, color).

If your team is attacking a number of product variation challenges, then read Keki Bhote’s World Class Quality for a highly effective approach.

This example shows a useful 5-Why format when multiple causes exist.  In this case, a top-level Pareto analysis showed that 35% of late shipments were caused by material shortages, and 14% were caused by downtime on a specific machine.  The 5-Why format is very useful in cases like this for identifying root causes.

5 why example when multiple causes exist

Here is the above analysis, with follow-up actions added to the document.

5-Why showing next steps

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