The Discounted Failure Pitfall for autonomous system safety

The Discounted Failure Pitfall: Arguing that something is safe because it has never failed before doesn't work if you keep ignoring its failures based on that reasoning. A particularly tricky pitfall occurs when a proven in use argument is based upon a lack of observed field failures when field failures have been systematically under-reported or even not reported at all. In this case, the argument is based upon faulty evidence. One way that this pitfall manifests in practice is that faults that result in low consequence failures tend to go unreported, with system redundancy tending to reduce the consequences of a typical incident. It can take time and effort to report failures, and there is little incentive to report each incident if the consequence is small, the system can readily continue service, and the subjective impression is that the system is perceived as overall safe. Perversely, reporting numerous recovered malfunctions or warnings can actually increa