This is about the logic of sufficiency and necessity, and it requires the skill to identify narrowly-scoped syllogisms for each step of the causal graph. For anyone really interested in this stuff, read about Theory of Constraints "Thinking Tools", and supplement with a smattering of simple philosophy, such as Hume's Guillotine and the Munchausen Trilemma. Basically, for any examination of "why did our actions result in this outcome", you're going to come down to a collection of premises, some of which are facts and others of which are values. Many of these values are obvious, widely-shared non-negotiable values, but others are slippery biases or assumptions that have snuck into the system, and focusing on one of these is often identified as the "root cause", even though there are by definition several; any one of which was sufficient to cause the outcome. Really "root cause" just means the identification of one value that could and should be changed, which thereby will propagate its changes throughout the causal network.

I will say though, that this is a difficult skill, and it takes practice, because there are so many personal biases that can creep in and lead to a corrupted causal analysis. It's also a bit thankless because once you come up with a decent root-cause analysis, it reads so clearly that it basically comes across as obvious and common-sense to anyone that reads it, leading them to underestimate just how much work it took to get there.