With this in place objects can only access their own private methods. This is a common feature in OO language, sometimes known as object private
When you build a class with this designation neither getters or setters are generated for the object.
If you have two car objects you will not be able to call
internal_model on the car objects from inside another car object (seems obvious). But since private fields behave this way exist a more restrictive methodoloy is needed.