When something goes wrong, managers often think they need to introduce a new procedure, or establish a new control to stop whatever it was from happening again.

But, unless they have been schooled in the theory of variation, managers don’t ask themselves: ‘was this a one-off, or is it likely to occur again?

In variation-speak it is to ask ‘was this a special cause or a common-cause event?’

Where things are predictably going wrong (common-cause events) it is right to make a change to stop things going wrong in the future.

But if we treat a one-off as though it is a predictable event, we simply make our organisations more complex and more prone to mistakes.