Now, I will allow that very complex systems can mask that root cause.
One might _never_ be able to find out the root 'why' for a number of reasons: lack of time, inability to see into the black box where the failure happened. Perhaps everyone is dead, the data you need destroyed, the widget is lost under the ocean.
And that sometimes the root cause failure isn't a hard technical thing but something squishy like 'we failed to budget for disk space' or 'the CIO insisted we do it that way'.
Of course the flip side is equally awful. When folk say "that's just how it works around here" you know you are doomed.