By the CIToolkit content team   |   3 minutes read

Why-Why Diagram

Why-Why Diagram

5 Whys is most effective when used to solve simple problems with a single root cause. Oftentimes, a problem is the result of multiple causes occurring together. Each cause is the result of a further cause or multiple causes. Each time you ask why, there might be more than one answer. Such hierarchical structure of potential causes can be represented in a fishbone diagram or a tree diagram called the Why-Why Diagram.

A why-why diagram is an extension of the 5 Whys approach where they are similar in that they both ask the same Why question multiple times. However, a why-why diagram is used to identify the root causes of a problem when there are multiple factors to consider. There may be multiple answers at each stage, and each of these answers need to go through a separate process of the why-whys analysis.

Why-Why Structure

In the why-why diagram, the problem will normally be placed on the left side of the diagram whereas the most specific causes will be placed on the right side. Lines can be used to connect related series of causes. The information in the why-why diagram is in fact the same as what you would find in a fishbone diagram, but the format is different. And like the fishbone diagram, potential causes can be organized into categories to provide better focus and easier reference.

Why-Why Diagram Formats
A why-why diagram can be represented in a fishbone diagram or a tree diagram

Drawing the Diagram

Why-Why Diagram

Why-why diagrams are often constructed during team brainstorming sessions. By going through the steps of drawing the diagram with your team, everyone gains a better understanding of the problem, making the solution easier to find later.

  • With your team, clearly state the problem then write it on a post-it card.
  • Place the problem card on the left side of a whiteboard or wall.
  • Ask ‘Why the problem occurs’. Let the team members write as many causes as possible on post-it cards, group similar causes together, then stick them up to the right of your problem.
  • Keep asking Why until the team identifies the root causes of the problem.
  • Once you are finished, discuss and agree on the corrective actions that will permanently solve the problem.

Note: You may need to collect and analyze data to confirm the identified root causes are real.


A restaurant team has constructed a why-why diagram to resolve a complaint regarding the increased number of customer complaints about the taste of the coffee they make.

Why-Why Diagram Example

Note that the team has identified six possible root causes which could be further investigated, and they were bordered in black.

Other Formats

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