For every complex problem, there is a simple and wrong answer.

For what it's worth, I think it's great that you are out there practicing and learning by trial and error; it takes time to learn the art of people skills and negotiation. Just thinking off the cuff here, but it seems to me there is a spectrum for how hard or soft one would want to negotiate depending on the specific situation, and it certainly takes into account how badly you want/need the job versus how badly the potential employer wants/needs you and what bargaining leverage each of you has. Given that this HR person easily ended the conversation, it tells me that they have other viable candidates and were ready and willing to move on if an applicant is not willing to acquiesce in this particular instance.