ISO 26262 functional safety assumes that systems operate safely if components do not fail mechanically or electrically. However, an autonomous vehicle camera blinded by direct low-angle sunset, or a radar confused by wet guardrail reflections, has zero component hardware faults yet produces life-threatening decisions. ISO 21448 (SOTIF) systematically minimizes the 'Unknown-Unsafe' operational scenarios.
The engineering goal of ISO 21448 is an iterative reduction loop: First, stress-testing discovers a scenario in Area 4 (e.g., a truck carrying reflective mirrors causing phantom braking). The scenario moves into Area 2 (Known Unsafe). Engineers then update perception filtering rules, modify the neural network dataset, or restrict the Operational Design Domain so that the hazard can never trigger an accident. Once validated across 100,000 simulated edge miles, the scenario transitions permanently into Area 1 (Known Safe).