So imagine a nuclear plant that saves costs by reducing safety margins. You have less redundancy in equipment and staff, less containment, or whatever. How do you accurately predict the risk? And what error would that risk have? Every single factor you are modifying can come together in weird combinations and has an error bar of its own. What happens when there is suicidal engineer + metal fatigue + unusual weather conditions? Ultimately this seems like a fools errand. The belt-and-braces approach is the only way humans have found to safely design complex inherently risky machines. And deviating from that creates Shuttle shaped clouds in the sky and Boeing shaped holes in the ground.