5. Five Whys
The Five Whys is an iterative problem-solving technique developed by Toyota, as part of their Toyota Production System manufacturing method. It is a simple technique where we keep asking Why, at each stage dissecting or deconstructing the answer and often it takes five or more times to drive down to a satisfactory root cause.
It is designed to be a simple technique that anyone can understand; there will often be more than five.
Taiichi Ohno
The inventor of the Five Whys technique, and also credited with devising the Kanban organisation method, used this original example:
Why did the robot stop? The circuit has overloaded, causing a fuse to blow.
Why is the circuit overloaded? There was insufficient lubrication on the bearings, so they locked up.
Why was there insufficient lubrication on the bearings? The oil pump on the robot is not circulating sufficient oil.
Why is the pump not circulating sufficient oil? The pump intake is clogged with metal shavings.
Why is the intake clogged with metal shavings? Because there is no filter on the pump.
This would fail any modern root cause analysis and manufacturing standards and would probably need a further three or four Whys.
Do not stop, five is a guide.
Those further Whys are not hard to find, and it is worth doing them here rather than leaving them as an exercise:
Why is there no filter on the pump? The pump was specified without one.
Why was it specified without one? The specification was copied from a machine working in a clean environment, where there is nothing for the intake to draw in.
Why did copying it go unchallenged? Nothing in our specification process asks what the machine's surroundings will be.
Now there is something to change, and it is not the pump. Ohno's five stop at a missing part. Three more arrive at a process that will fit the same missing part to the next machine, and the one after that.
Most events need two chains rather than one, and running only the first is how a CoE arrives at an answer that prevents nothing. The first chain asks why the failure happened. The second asks why we did not know about it, and it has a different root cause and usually different Next Actions. A team that follows only the first will find out about the next one exactly the way it found out about this one.
Why did you miss the meeting? I was late for work and got a later train.
Why were you late for work? I woke up late for work.
Why did you sleep late? My alarm clock didn't go off.
Why did the alarm clock fail? The battery was flat.
Why was the battery flat? I was not monitoring it, and did not check the night before.
The root cause is the failure to maintain the clock and the lack of any backup.
We have gone far enough when the answer is something we can change, and when changing it would have prevented the class of failure rather than this instance of it. A chain that ends at a person has probably stopped one Why short.