One lesson from the study of complex systems is that there is almost never a single root cause. Really bad failures only happen because several things conspire.
I think this is a pretty interesting point that I’ve also observed from the port-mortems of every company I’ve ever worked at.
Current thinking from folks such as John Allspaw, Dave Zwieback, Richard Cook, Sidney Dekker, et al, is that the “five whys” is not a good way to deal with failure as it tends to come down to people rather than the complex system. Of course, this post is originally from 2011, so lots of thinking around this has changed – hopefully for the better.