I believe for the most part this is true...you cannot change unless you first admit you have a problem. No matter how much nagging you do, if they don't truly want to change they will simply block you out. They've heard it all before. Unfortunately many have to hit rock bottom before that change begins. That's not saying you should give up on the person by any means, but just have an awareness that it's not your fault that they are not changing and it's something they must come to on their own.