See also "The problem with ‘5 whys’" by Alan J. Card [1] [2]. I've included some quotations below. The discussion of "distal causes" is illuminating.
[1] https://qualitysafety.bmj.com/content/26/8/671
[2] http://dx.doi.org/10.1136/bmjqs-2016-005849
> The ‘5 whys’ technique is one of the most widely taught approaches to root-cause analysis (RCA) in healthcare. Its use is promoted by the WHO, the English National Health Service, the Institute for Healthcare Improvement, the Joint Commission and many other organisations in the field of healthcare quality and safety. Like most such tools, though, its popularity is not the result of any evidence that it is effective. Instead, it probably owes its place in the curriculum and practice of RCA to a combination of pedigree, simplicity and pedagogy.
> In terms of pedigree, ‘5 whys’ traces its roots back to the Toyota Production System (TPS). It also plays a key role in Lean (a generic version of TPS) as well as Six Sigma,11 another popular quality improvement (QI) methodology. Taiichi Ohno describes ‘5 whys’ as central to the TPS methodology:
The basis of Toyota's scientific approach is to ask why five times whenever we find a problem … By repeating why five times, the nature of the problem as well as its solution becomes clear. The solution, or the how-to, is designated as ‘1H.’ Thus, ‘Five whys equal one how’ (5W=1H). (ref. 9, p. 123)
> This quote also makes the case for the technique's simplicity. Asking ‘why’ five times allows users to arrive at a single root cause that might not have been obvious at the outset. It may also inspire a single solution to address that root cause (though it is not clear that the ‘1H’ side of the equation has been adopted as widely).
> ...
> It is clear from the tree diagram that the causal pathway related to the wristband printer is neither the only relevant cause of the incident nor indisputably the most important. A serious effort to solve the myriad problems that gave rise to this incident would have to tackle a number of other causal pathways as well.
> ...
> There are many ‘correct’ ways a team might use ‘5 whys’ to assess even this one incident. And it is unlikely that any two teams would independently arrive at exactly the same results. This subjectivity is critically important because ‘5 whys’ focuses on only one root cause at the end of one causal pathway.
> ...
> Targeting only the most distal cause
> Not only are users of ‘5 whys’ limited to one root cause per causal pathway, but they are also limited to selecting only the most distal cause (conventionally, the fifth ‘why’). There is, however, no logical reason to assume that this is always the most effective or most efficient target for intervention.
> Actually, if it were possible to magically place a 100% effective risk control at any one point on the tree diagram, it would be best used on a proximate cause. For instance, making it impossible to administer medication without checking the wristband would render all the more distal causes moot for the purpose of preventing a recurrence.
> And, while 100% effective risk controls are seldom available, an action plan that includes a proven26 (if certainly imperfect) intervention like a well-designed bar-code reader with a forcing function for patient identification (ID) is more likely to prevent another serious ‘wrong patient’ medication error than switching to a well-designed printer.
> This is not to suggest that more distal causes are not appropriate targets for improvement efforts. In the example presented in figure 1, for instance, there is clearly a profound need to change the culture from one that is task-oriented and sometimes hostile to one that is outcomes-oriented and psychologically safe. The pervasive impact of such a culture change would be far more important than merely reducing the risk that this particular incident might recur; it would influence almost every quality and safety issue in the organisation.
> And, in contrast to that powerful-but-difficult lever for shifting outcomes, sometimes more distal causes represent ‘low-hanging fruit’ that can be addressed while a more proximate solution is in the works. In figure 1, educating patients about why clinicians will be constantly asking them to identify themselves would be far from foolproof. But it would be fast, cheap and easy. And it might reduce an important barrier to best practice in verbal identification.
> Appropriate targets for intervention may occur anywhere along the causal continuum and on any causal pathway. And efforts to improve safety and quality will often require more than one intervention targeting more than one underlying hazard. It is useful to identify all the key hazards that gave rise to an incident and ensure that each of these is either addressed or intentionally accepted. (See, for instance, the Options Evaluation Matrix.) But the use of ‘5 whys’ makes this impossible.