[candu]

That's the good old Pareto principle for you: the last few percent are going to take a lot more effort than the first 95%.

More to the point, this falls into the category of safety-critical systems, with the added wrinkle of potentially being used daily by millions of people. Unlike many domains where software is applied, 80% of the way there doesn't cut it, nor does 95% or 99% or even 99.9%.

(Leaving aside the fact that, for all of us not actively engaged in autonomous vehicle R&D, we likely have absolutely no idea how close we are to success here, or even what all the relevant goalposts would be.)