Just to put a few thoughts more about causes into circulation:
Suppose I have a job which requires me to walk 20 meters along a horizontal bridge made out of a tree trunk of 20 centimeters diameter.
The SOPs say how I am to do it.
Sometimes my pole lies on firm, sandy ground.
Sometimes my pole is suspended 1 m above a marsh.
Sometimes my pole is suspended 100 m above a boiling geyser.
General human factors stuff tells us that one in a thousand attempts I will fall off. Of course, there are some pole walkers that never fall off. And there are some pole walkers that falls off one in a hundred attempts. And 80% of pole walkers believe they fall into the first category, not the second.
Somebody walks on the pole 100 m above the boiling geyser, falls off.
Some of his fellows say: he's obviously not "first category" material. Shouldn't have fallen off. We do our best never to fall off and cannot understand why he did. We advise all our fellow pole-walkers not to fall off. Don't do it. Ever.
Some of his fellows say: well, he certainly shouldn't have fallen off, but he did. We don't intend to, and do our best not to, but maybe his shoes weren't quite right; they are not as good as we think ours are. And maybe when he wobbled a little and tried to correct his stance, his shoes deformed and he lost his balance. We won't use those shoes.
Some of his fellows say: you fall off a pole generally once in a thousand attempts. Our career is comprised of 500 pole-walkings. We have a one-in-two chance of falling off. So we'll go on the firm, sandy ground. We'll even go on the 1m above the marsh. But there is no way we are ever going to do the 100m above the boiling geyser. Forget it.
Question: who has the surest way of avoiding killing himherself?
Another question: Is the "primary cause" the failure to keep balance; or is it the wrong shoes; or is it the situation (100 m above the boiling geyser)? Or is it all three? Or is it some combination?
A further question: who is "responsible" for the accident?
The pole walker? Hisher shoe manufactuer? Or his employer who requires himher to walk 100 m above a boiling geyser?
We have seen examples of all three of these causal points of view in this discussion. Who is right? Is anybody right? Or are they all missing understanding something about causes?
PBL