You know you have negotiated a good deal when both parties walk away feeling just a little bit of pain. To create a good, long-term relationship with the people you are negotiating with, you must make them feel like they got a good deal too. If you push for everything and give in on nothing, you might feel great, but the other party feels horrible about the deal.
The art of negotiating is in finding that balance where you give enough to keep the other party motivated and interested in not only getting the deal done but feels good about doing business with you in the future (or would tell their friends to do business with you).
I have seen in my career that a hard-fought negotiation strengthens the relationship between the two parties. And when the deal is done, you both get to celebrate its success.
Pro Tip: Always have a few items when you are heading into a negotiation that are a list of things that are non-negotiable, and others that might not be so important to you. They might be important to the other party, but you’d be willing to give up to make the deal.