Understand
Five whys
Ask why a problem happened, then why that happened, until you reach a cause you can fix rather than a symptom.
- Time15 to 30 minutes
- People2 to 8 people
- Steps4
What it's for
Use it after an incident or for a problem that keeps coming back. The first answer to "why" is almost always a symptom. Asking again, about four more times, moves the conversation from who made a mistake to what in the system let it happen.
Five is a rule of thumb. Stop when you reach a cause that, if fixed, would stop the problem recurring.
How to run it
State the problem3 min
Write what happened as a fact, without blame.
Ask why, five times15 min
Answer each why with the cause of the one above it.
Agree the root cause5 min
Check the chain reads back as "because" from bottom to top.
Decide the fix5 min
One action that addresses the root cause, with an owner.
Tips
- If an answer is a person, ask why the system let that person make the mistake.
- Problems often have more than one cause. Branch the chain rather than forcing a single line.
Where it comes from
Developed by Sakichi Toyoda and used inside Toyota, where Taiichi Ohno made it part of the Toyota Production System. Ohno described it in his book Toyota Production System (1978).
Pairs well with
Fishbone diagram
Sort the possible causes of a problem into categories along the bones of a fish, so the team looks wider than the first cause it thinks of.
Premortem
Imagine the project has failed, then work out why, so risks get named while there is still time to act on them.
How might we
Turn problems and insights into questions that start with "How might we", which invite ideas instead of arguments.