Two opposite directions of reliability thinking — and why safety-critical industries insist on doing both.
Put an FMEA worksheet next to a fault tree diagram and, at a glance, they can look like two ways of writing down the same information. They aren't. FMEA starts at the smallest scale — one component, one failure mode — and works upward, asking what would happen to the system if that specific part failed that specific way. Fault Tree Analysis starts at the largest scale — one specific, already-chosen catastrophe — and works downward, asking exactly which combination of lower-level failures would have to happen together to cause it. Same underlying failures, opposite direction of reasoning, and each method is structurally blind to something the other one catches.