With persistence comes self-confidence: the belief that you can do it.
It doesn’t matter how many times the other person says no, disagrees with you, or gives you a hard time. Keep asking, and stay focused on your goals (without making yourself the issue). Persistence, after all, is a focused effort, over time, to meet your goals.
Persistence is key in negotiation. Keep finding ways to get more information and unlock new value levers for both parties. Your persistence will pay off in the long run.