A cause and effect diagram, often called a “fishbone” diagram, can help the team in brainstorming possible causes of a problem by sorting ideas into useful categories. A fishbone diagram is a visual way to look at cause and effect.

The “head” of the fish is the “effect” – eg: the car won’t start

The “body” of the fish are the potential “causes”.

Brainstorm the major categories of causes of the problem. Here are some examples of generic headings:
Machines (equipment)
People (manpower)
Write the categories of causes as “bones” of the fish.

Brainstorm all the possible causes of the problem. Ask “Why does this happen?” As each idea is given, the facilitator writes it as a branch from the appropriate category. Causes can be written in several places if they relate to several categories.

Again ask “Why does this happen?” about each cause. Write sub-causes branching off the causes. Continue to ask “Why?” and generate deeper levels of causes. Layers of branches indicate causal relationships.
When the group runs out of ideas, focus attention to places on the chart where ideas are few.