Yes but what I'm saying is you don't need 9 9s of good driving in order to get 9 9s of accident-free driving. You only have an accident when you're driving badly and are exceptionally unlucky (I suppose the amount of bad luck required decreases as the badness of the driving increases).
In the scenario I mentioned you'd have at best a 50% duty cycle of good driving, but the accident rate would be substantially lower than 50% every 10 seconds.
In the scenario I mentioned you'd have at best a 50% duty cycle of good driving, but the accident rate would be substantially lower than 50% every 10 seconds.