A while back I tried running Toyota’s full 5-whys process on every problem that came up on a particular project. Each time through, we found that the fourth and fifth levels regularly came up with the same old reasons – to such an extent that the process became somewhat devalued for us. Don’t get me wrong, we did find valuable insights some of the time, and consequently we were able to permanently eliminate some classes of problem. But usually those insights and fixes came from our values (ie. automate everything, test everything etc), and not really from the process itself. I have only rarely used full-on 5-whys since, preferring an informal team workshop approach to fixing root causes.

But recently I’ve been looking at Current Reality Trees (CRTs) from the Theory of Constraints. The main difference, it seems to me, is that a CRT begins with around ten undesirable effects (UDEs), whereas 5-whys begins with only one. So in a CRT, the interplay between the numerous problems seems likely to get to the common core of the problem more quickly. And that core problem is instantly validated, because we’ve derived it in such a way that we know it is relevant to many problems.

If you’ve used both techniques, did you find one more successful than the other? Did one generate more convincing results? Or are they answering different questions, and should they therefore be used in different contexts?