If you drive defensively (if you've ever been a motorcyclist you'll know what I mean) then you can avoid accidents which nonetheless would not of been your fault. Thus, any accident is an _indicator_ (but not a perfect one) that you may not be the best of drivers.

An example might be the very common rear-end shunt at a roundabout (or "circle" in South Africa, not sure if you have 'em in the US) - an experienced driver will [usually] pull away confidently without hesitating. A less experienced driver can misjudge more often and set off only to suddenly stop, leaving the car behind to crash into them. Strictly road-lore says the rear driver should have observed better, they are liable as they crashed into a [near] stationary vehicle - but the foremost driver is hardly without blame. Yes, the rear vehicles insurance pays out for all damage; but the insurer of the front vehicle would be right in judging them a greater insurance _risk_.

It doesn't always work (some good drivers will just get unlucky and be hit by cars they can't avoid) but that's a rough version of a rationale.