The word ‘cause’ has an air of finality about it that discourages further investigation. If a pipe fails, for example, and the cause is said to be corrosion we are tempted to think that we know why it failed. But to say that a pipe failure was due to corrosion is rather like saying that a fall was due to gravity. It may be true but it does not help us to prevent further failures. We need to know the answers to many more questions: Was the material of construction specified correctly? Was the specified material actually used? Were operating conditions the same as those assumed by the designers? What corrosion monitoring did they ask for? Was it carried out? Were the results ignored? And so on.