5 Whys is a technique used to clarify the root causes of an issue. It involves asking "Why?" five times to the previous "Why". Depending on problem's complexity, more or less than 5 whys may need to be asked.
5 Whys Examples
Let us explore how the 5 Whys are applied, and how problems of different complexity lead to differing results.
Problem: A small electric motor keeps overheating.
Why is the motor overheating?
Because the motor is working harder than it was designed to.
Why is it working too hard?
Because the fan it drives is clogged with dust, adding extra resistance.
Why is the fan clogged with dust?
Because it hasn't been cleaned or inspected for a long time.
Why wasn't it cleaned or inspected?
Because there's no maintenance schedule in place for small auxiliary equipment.
Why is there no maintenance schedule?
Because small equipment was overlooked when creating maintenance protocols.
Root Cause: There's no maintenance schedule in place for small auxiliary equipment.
The 5 WHYs example is the namesake for the 5 WHYs technique. It highlights how a root cause is identified through asking WHY five times.
Problem: The car stopped on the highway.
Why did the car stop?
Because it ran out of fuel.
Why did it run out of fuel?
Because I didn't fill up the tank.
Why didn't you fill up the tank?
Because I forgot to check the fuel gauge before leaving.
Root Cause: I forgot to check the fuel gauge before leaving.
For simpler problems, a root cause will be found through FEWER whys.
Problem: A product fails quality inspection.
Why did the product fail quality inspection?
Because there were surface defects on the component.
Why were there surface defects?
Because the molding temperature was inconsistent.
Why was the temperature inconsistent?
Because the heating element was malfunctioning.
...
Why was the schedule not followed?
Because maintenance records were not being tracked properly.
Why weren't records tracked properly?
Because the tracking system was outdated and difficult to use.
Root Cause: The tracking system was outdated and difficult to use.
For complex problems, MORE whys must be asked to reach a root cause. Often, there may be multiple.
Problem: A project missed its deadline.
Why did the project miss its deadline?
Because key tasks were delayed.
Why were key tasks delayed?
Because resources were unavailable.
Why were resources unavailable?
Because of competing priorities and understaffing.
Why were there competing priorities? (Branch I)
Because project planning didn't account for other ongoing work.
Why was there understaffing? (Branch II)
Because hiring was frozen due to budget constraints.
Root Causes: Poor project planning and budget constraints causing understaffing.
When a problem has multiple root causes. For many problems, this will be the case.
The Limitations of 5 Whys
Whilst the 5 Whys tool can be helpful, it faces several limitations. It is vital that this technique is applied where appropriate. It is not an all-encompassing tool, but it can be useful for identifying root causes in many situations.
The Limitations of 5 Whys include:
Possibility to identify symptoms whilst failing to establish root causes.
An investigator being unable to identify causes they don't know/understand.
Results aren't repeatable, and different individuals may think of different causes.
Potential to neglect other causes where multiple are present.