silent failure
termA fault that produces no error anywhere: the system completes its work, reports success, and does the wrong thing.
The defining property is not that the failure is small but that nothing in the system disagrees with it. An access point given a DHCP option 43 value in another vendor's encoding completes its lease, reads a value it cannot parse, and never joins a controller. A firewall rule shadowed by a broader rule above it is correct, enabled, and never evaluated, and Palo Alto's own documentation notes that Commit and Push does not report shadowing. A security signature left in staging appears in the log, contributes to a request's rating, and blocks nothing. In each case the artefact everyone inspects looks right, because it is right; what changed is the thing reading it. The diagnostic cost is what makes the category worth naming: an error message points at itself, so the work is repair. A silent failure points at nothing, so the work is first proving which of the things that appear to be working actually is. Guardrails that only report problems are therefore weaker than they look, and a check that passes on an empty input, a missing file or an unparsed regex is itself a silent failure wearing a green tick.
Also known as: silent failures, fails silently, fails open, silent breakage, no error