It's not about harder but about what error you can tolerate. Here if you have accuracy 99% for many applications it's enough. If you have 99% accuracy per trip of no crash during self driving then you gonna be dead within a year very likely.
For cars we need accuracy at least 99.99% and that's very hard.
I doubt most people have 99% accuracy. The threshold of tolerance for error is just much lower for any self-driving system (and with good reason, because we're not familiar with them yet).
I guess something like success rate for a trip (or mile) would be a more reasonable metric. Most people have a success rate far higher than 99% for averages trips.
Most people who commute daily are probably doing something like a 1000 car rides a year and have minor accidents every few years. 99% success rates would mean monthly accidents.
