The “5” is a reminder to avoid shallow attribution
When faced with a problem, there’s a general tendency for people to only consider the immediate contributing factors.
The “5” in “5 Whys” is a reminder to go beyond shallow attribution and keep exploring underlying causes.
“5” is a heuristic not a fixed number
In practice, the number of whys can be less or more than 5. Because of the tendency to be shallow, I’d still suggest thinking about it more if it ends up being less than 5.
5 Whys, not 5 Whos
The use of “why” is to remind us not to default to blaming people, especially their motivation (aka fundamental attribution error), and consider broader factors for why something happened.
See also Six Sources of Influence.
“How” seems clearer than “Why”
The purpose of root cause analysis is to understand mechanism(s) to allow us to come up with better ideas for how to intervene. “How” expresses this more clearly than “Why”.
See also “Why” is about purpose; “How” is about mechanism.
But there’s usually more than one root cause!
There is no assumption that there is a single root cause. It’s not called “single root cause analysis”.
The idea is that you’re exploring a single promising factor with 5 Whys. This does not mean you won’t explore more.
To reliably interrupt a mechanism, intervene at multiple points, not just the “root cause”
If you want to reliably interrupt a mechanism, you should do it at multiple points. This is because no countermeasure is perfect and layered defense is an effective meta-countermeasure for this.
Example borrowed from The Five Whys for Start-Ups by Eric Ries.
You don’t actually need to address every contributing factor
You don’t actually need, nor want, to address every contributing factor because the possible countermeasures may be expensive, and unnecessary if other cheaper factors are addressed.
But it’s too simple to work for complex problems!
Every organisation has problems at different levels
If you look at any organisation, problems are happening all the time at different levels. Typically, in terms of numbers, most problems are simple, the least problems are complex, and complicated problems are somewhere in the middle.
Use the simplest method that is useful (including fitting within the time you have available)
Simple problems can be addressed with simpler methods (like 5 Whys), while complicated and complex problems warrant more sophisticated methods. It’s not useful to apply the same root cause analysis / problem-solving approaches for complex problems as you would simple problems.
5 Whys is not intended for complex problems; sophisticated, time-intensive causal analysis is not intended for simple problems.
To learn more
Find some 10+ year Toyota person to talk to. They’ll probably have more insight than I have.
