I assume occasional mistakes are treated differently than negligence, willfully going against policy, or multiple failures from the same person (i.e. a pattern

I assume occasional mistakes are treated differently than negligence, willfully going against policy, or multiple failures from the same person (i.e. a pattern of failure, perhaps just incompetence). I'd be interested in the cases when even a company that practices no-blame post-mortems has to fire the people who screw up multiple times.