Dealing with risks
Motorcycle accidents happen for a variety of reasons; all can be prevented simply by not riding. If you ride, you face the probability of having an accident. You can change that probability, but can not make it go away unless you quit riding.
I have fallen on my Ninja 250 twice. Both were my fault. Most recently the chain jumped the sprocket and got caught between the swingarm and sprocket. I was riding at roughly 10 mph while going around a corner when it happened. I was two blocks from home and hoped to make it the rest of the way. Yes it was my fault, yes I was pushing it too far, and given the same situation I would do it again.
The other time I was backing out of the driveway with two inches of snow on the ground. The rear tire made contact with the sloped edge and slid sideways, I slipped when trying to catch it and fell down. I was straddle walking it backwards at the time, how much slower should I have been going? It was my fault, I was pushing it too far, and I have done that again several times without incident.
In Washington DC, a few years ago, I made the mistake of stopping as the light turned from yellow to red. I was rear-ended hard enough to get knocked in to the middle of the intersection. I should have known better than to brake that hard in the city; I screwed up bad. Since it was a rear-end collision and a witness saw that the light was changing, the other driver's insurance paid for the damage to my bike. From the insurance company's point of view, the accident was clearly the fault of the other driver, but I haven't allowed that to happen again.
Riding a motorcycle is dangerous. There are a lot of things you can do to be safer (go to school, keep your equipment in good repair), and there are a lot of things you can do that improve your riding ability which paradoxically put you in danger of crashing (riding in the snow, following better riders in curves), but to make blanket statements that you should never crash due to your own mistakes or that all riders will crash simply doesn't work.