FMEA — Failure Mode and Effects Analysis — works through how a process or product could fail, what each failure would cause, how likely it is, and how likely it is to be caught before it matters.
Severity, occurrence and detection are scored and multiplied into a risk priority number used to rank what to address. The RPN is a sorting device and not much more: it compresses three different quantities into one and is easily gamed by nudging a score. A severity of 10 warrants attention regardless of what the product comes to.
Its value is being done before anything goes wrong. Most quality work is reactive — a defect appears and gets analysed — and FMEA is one of the few structured chances to reason about failure while changes are still cheap.
It fails as a document rather than as a method. Completed for a customer audit and filed, it consumes days and changes nothing. It only earns its cost when the high-risk rows produce actual countermeasures and it is revisited when the process changes.
