Five whys
A technique for finding the root cause of a problem by asking “why?” several times in a row, each time about the previous answer.
What it’s for
It keeps you from stopping at the symptom and helps you fix the underlying cause.
Key elements
Concrete facts
Start from a problem described with facts, not opinions.
On the previous answer
Each “why?” is asked about the last answer.
Causes, not culprits
The chain looks for what failed in the process, not whom to blame.
An example
Taiichi Ohno’s classic example: a machine has stopped.
Each “why?” goes down one level, until you reach something that, once corrected, keeps the problem from happening again.
How it’s done
Describe the problem with concrete facts.
Ask “why?” about each answer.
Stop when you reach a cause that can be corrected.
Applications in design
When to use it
In synthesis, to move from a problem you see to the cause behind it.
Avoid
Following a single chain of causes when the problem has several.
Don’t fall for it
Five is a guideline: sometimes three whys are enough and sometimes you need more.
Connections
Related to
Authors and works
- 1988
Taiichi Ohno
Spread it as part of the Toyota Production System.
Sources
Original sources
- Ohno, T. (1988). Toyota production system: Beyond large-scale production. Productivity Press.
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