100% accuracy is impossible, simply because no situation can be reproduced with 100% accuracy, not in real life and not in a computer simulation.
That's not the point, though, the point is getting as close as possible to the real thing. Sure, there are some limitations, even with very expensive and complex motion simulators, but in return a crash won't kill or injure you (although with the right motion sim, it could) and you don't have to worry about the (financial) damage and the expenses of obtaining and running several different cars.