5 stars isn't perfect. 5 stars is "there's nothing so bad that I want to take the time to complain about it."
Waymo employees, who are encouraged to be especially tough, give reviews that are 47% negative. That's likely closer to the metric for perfect.
We don't get perfection from human drivers either, of course. Though part of the promise of Waymo is much better performance than humans, which it apparently isn't close to yet. And this data is for relatively common cases: for the long tail, one-in-a-million case, the conventional wisdom is that humans would do better.
For entirely different reasons, though. Your taxi driver is not going to randomly freak out because they mistook a bush for a pedestrian or didn't understand what traffic cones mean. The bad taxi driver is just going to drive too fast while talking on their cellphone.
