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Subjectivity in Thinking About Causes
This pitfall is harder to appreciate in a case analysis unless one does some role playing with only certain kinds of information available to each individual in the role play. If you have read all of the Therac-25 case we present, you have a "god's eye view" of the action, like the reader of a classic novel. But the people inside the case never had the convenience of this view, and might not even be able to agree now on a single hindsight-driven account after the fact.
Once you can firmly grasp the limited nature of each individual’s knowledge about what was going on at any particular time, you can then progress to further ambiguity about how people might be personally or professionally motivated to find one kind of cause for an accident more likely than another. It may be that the AECL technicians were simply handicapped by their limited knowledge when they thought an electric shock might be the cause of the first accident in Tyler, TX. But it was also a convenient cause in that it was not AECL's problem.
A note of caution here. It is easy to become cynical and to invent conspiracies and evil motivation for everyone. Resist this temptation. Cynicism is the easy way to appear sophisticated about a case, but it is often misleading. Most people, most of the time, at least think they are not harming others by their actions. When you find the opportunity for a motivated distortion of the causes of an accident, note it, and ask yourself how that person could maintain the distortion while still thinking well of themselves.