In disciplining children, one has to muster the best form of self-control. Whether to give in to the child's wants or putting your firm hand down on a decision should entail a lot of introspection. There are times when you have to give in to the child. This should not however serve to make the child know that he/she is superior than the disciplining authority. But only to make him learn that he is given importance depending on what he likes or doesnot like. But if its a totally no-deserving decision, the desciplining person should never wane and really put a firm fist down!

My cousin and his whole family (wife, mom, and dad) are trying to be firm and not to give in to his 9 year old son... He is a good boy, but he has "his moments," and when those moments come, he can outstubborn the four adults around him!

If you start to give in when the child is a young age, they learn the behaviors they need to do in order for you to continue to give in. I beleive that parents should stick with their decisions. If I tell my daughter no, the answer is no and she knows not to take it any further.

I agree with that. Children should learn fairly quickly that when their parent says no, that's exactly what they mean.