Thanks to Mike for reminding me about the 5 whys process. A simple, yet very effective way of getting to the root cause of a problem by iteratively asking why five times, each question forming the basis of the next question. It was originally used by Toyota as a technique for problem solving in their manufacturing process, and was one of the fundamental techniques in their scientific approach. This is an example they give of how it might be used in one of their plants:
As this Buffer post on the 5 Whys points out, the method is also popular in Lean development to establish the root cause of defects, problems or just when something unexpected happens. Really useful reminder.