The Field Guide to Understanding 'Human Error'

by Sidney Dekker

There is no “root” cause So what is the cause of the accident? This question is just as bizarre as asking what the cause is of not having an accident. There is no single cause—neither for failure, nor for success. In order to push a well-defended system over the edge (or make it work safely), a large number of contributory factors are necessary and only jointly sufficient. How is it that a mishap gives you so many causes to choose from? Part of the story is the sheer complexity of the systems that we have put together, and that we have protected our systems so well against failure. A lot needs to go wrong for an incident or accident to occur. So you can really construct “causes” from everywhere. The causal web quickly multiplies and fans out, like cracks in a window. What you call “root cause” is simply the place where you stop looking any further. That means that any policy or standard that gets you to identify root causes, or probable causes, is of necessity: Cause is not something you find. Cause is something you construct. • Selective. There are only so many things you can label “causal” before the word “causal” becomes meaningless. • Exclusive. They leave out factors that were also necessary and only jointly sufficient to “cause” the failure. • Oversimplified. They highlight only a few hotspots in a long, twisted and highly interconnected, much finer-grained web that spreads far outside the causes you come up with. If you find a root or primary or...