Agreed. Zero tolerance (or 100% reliability) necessarily has infinite cost and/or takes infinite time. We need to be reasonable about our expectations for autonomous systems.

That said, what's the likely accident rate for a 95th percentile human, starting in a parked car, hitting another stationary vehicle parked directly in front of them? There must be a few "accidentally put it in drive instead of reverse" type incidents but I'd except it to be exceedingly rare.