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Every filter makes two kinds of mistake: it passes noise (a false positive) or it blocks signal (a false negative). Signal detection theory proves you cannot minimize both with one filter — tightening against one failure loosens the other. Filtering skill is not building a perfect filter; it is choosing, per filter, which failure is cheap and which is catastrophic, and tuning toward the cheap one.
No single filter can be both safe and selective — but a cascade of filters can. The design law that makes cascades work: optimize for recall at the bottom (capture wide, miss nothing, trust nothing) and for precision at the top (only the verified reaches you). Every serious signal-processing system on earth — spam pipelines, particle detectors, immune systems — is built this way, and your information system should be too.