That is what I'm always told. I've taken several safety courses for the beginners motorcycle course, advanced riders course, and a couple of company managed courses when I worked for companies and was provided company cars. Every one of then have stated that "all accidents are preventable". I've always called BS on that. I've had a couple of accidents, in cars, that I see no way that I could have prevented. Here is a video of a motorcycle accident that I honestly don't see how it could have been prevented. Sorry, I suppose that those of you who do not have a Facebook account won't be able to see it. The fact is, not all accidents are preventable short of staying home in bed and wrapped in bubble wrap. Even then, things could happen.
https://www.facebook.com/reel/872221967477962?mibextid=0NULKw&fs=e&s=TIeQ9V