Unless the computer malfunctions due to age and wear, which is a nontrivial concern.
Or it doesn't understand its driving into an accident, like that tesla driver who had his top half sheared off by a semi.
Or maybe the simple fact that nobody tests these things in a chicago blizzard, where snow sticking and freezing to the car could obscure sensors while said sensors have trouble even telling where the road is due to all the snow.
Im optimistic about this technology, but true 100% autonomous 100% safe cars are a pipe dream.
Ah well the Tesla car was level 2, which basically means "you should never not watch the road" - which is part of the problem, because people stop watching the road after like 5 minutes.
Additionally, self driving cars as of last winter have started to be tested in wintery conditions - conditions which they will stress test significantly.
In the end, the amount of 'human error' we deal with on a daily basis is sooo vast, maybe machines will also have errors - but the number will be significantly smaller.