Also called 5 whys, root cause analysis, why-why
What are the five whys?
Asking why repeatedly until you reach a cause you can actually fix, rather than stopping at the first answer.
What else it is called
- Other names
- 5 whys, root cause analysis, why-why
- In French
- les cinq pourquoi
Related entries
Understanding five whys
The machine stopped. Why? The fuse blew. Why? The bearing seized. Why? It was not lubricated. Why? The lubrication pump is not pumping. Why? The pump intake is clogged with swarf and there is no filter. Replace the fuse and you are back next week. Fit a filter and the problem is gone.
The common failure is stopping at the first answer, which is usually a person: operator error, somebody forgot. That is where an investigation ends if the culture punishes the answer, and it guarantees a repeat. The useful rule is that if your answer is a name, keep going, because the real question is what let a normal human mistake turn into a failure.
It also has limits. Five whys follows one chain. Where several causes interact, or where the data is noisy, you need something more structured.
In practice
The test of a finished analysis: does the fix change a physical thing, a design or a procedure? If the fix is "remind the team", nothing has been found.
Frequently asked
Does it have to be exactly five?
No. Five is a reminder that the first two answers are usually symptoms. Sometimes you reach a fixable cause in three, and sometimes you are still going at seven.