"Root cause" is a popular term among safety professionals, especially when conducting an "accident investigation" (which I prefer calling an "incident analysis"). For many safety pros the primary objective of an incident analysis is to find the root cause - the single most critical factor that caused the incident. They examine the setting carefully and solicit opinions from everyone who might have seen the incident. "Ask people 'why?' five times," claim some consultants, and you will get at the root cause.
I hope you see how silly it is to believe the root cause of something can be discovered by obtaining five successive answers to: "Why did this happen?" But can I convince you that there is really not one root cause to uncover - at least not with the methods typically used for an incident analysis (such as perception surveys and interpersonal conversations)?