Most Americans simply don't negotiate and even look on negotiation as a "bad thing". Last week there was a letter to one of the advice columns (I don't recall which) from someone who was upset that a friend was so ruse as to negotiate a better price on some item from a local merchant. Said that the negotiation was rude and embarrassing and that it was essentially stealing from the small merchant.
And the columnist agreed!
I was simply stunned. I am a terrible negotiator, but I know I should do so and never thought of it as rude. The vendor is welcome to say "No, the price is fixed."... and they almost never do so. In many cases the posted price is well over when the merchant needs to make a profit and has a "real" price that is acceptable.
Employers look at it the same way. If they can get you cheap, they are happy. At some point they will decide that you are not worth it. Negotiation is simply a matter of agreeing a a "price point" that is within the a range acceptable to both parties.That may be the empty set.
If you really want or need the job, you need to be less aggressive and make sure that the set is not empty. But a good negotiator can almost always reach a point that is better then the first offer by a significant amount.