[Double_Cast]

A literal trigger is a lever that fires a gun. A figurative trigger is some event that sets in motion a cascade of events that occur in rapid succession. The root cause of firing a gun would probably be analogous to loading the chamber with a live round. Which may have occurred hours, days, months, etc before the trigger was pulled.

I think the distinction is that the "trigger" relates to a particular instance of failure, whereas the "root cause" relates to a class of failures.