Root cause analysis is the structured search for why something actually went wrong — as opposed to the first explanation that sounds reasonable.
Why it is usually done badly
The most common root cause recorded in quality systems worldwide is “human error”. It is almost never a root cause. People make mistakes constantly; a well-designed process expects that and catches them. If a single person’s slip could produce the failure, the real question is why nothing caught it.
The second most common is “lack of training”, which is only a root cause if the person genuinely did not know what to do. If they knew and did it anyway, training will not fix it.
Methods
Five whys — ask why repeatedly until you reach something you can actually change. Cheap, fast, adequate for most issues. Its weakness is that it follows a single chain and can miss contributing factors.
Fishbone (Ishikawa) — map possible causes across categories such as method, machine, material, people, measurement and environment. Better when the cause is genuinely unclear.
Fault tree — work backwards from the failure through the logical combinations that could produce it. Used where consequences are severe.
No standard requires a specific method. What auditors look for is evidence that you looked past the obvious.
The test
A useful root cause is one you can act on. “The operator was distracted” is not actionable. “The two parts are visually identical and stored in adjacent bins with no verification step” is — and it suggests its own fix.