How does inertia affect a person who is not wearing a seatbelt during the collision

The law of inertia states that an object at rest will stay at rest or an object in motion will remain in motion until acted on by an equal or opposite force so when you are in a car that is traveling 60 mph your body is also traveling 60 mph and when you get into a wreck your seat belt is the opposite force against you that stops you from going through the windshield.