For a negotiation to be successful, it must end in agreement. As the saying goes, you can lead a horse to water but you can't make him drink. He has to want to take a drink.
The parties to any agreement both have to be willing to sign. This is different than wanting to sign. An agreement does not necessarily need to be equally satisfying. It just needs to be agreed to. Negotiators and mediators know that disparity of satisfaction has little to do with getting the parties to agree.
What is important is that both sides, individually, feel that they have gotten something out of the agreement.
Timing is everything. Agreements shouldn't be rushed. But a negotiator can prepare the way to reach an accord. Effective mediators and negotiators know this and use the negotiating process as a means to building an environment that promotes agreement.
Practice makes perfect. Actually, we all learn by practicing. Getting the parties comfortable with committing is part of achieving a global accord. All too often a negotiator tries to rush to an agreement only to be frustrated when the other person pulls back at the last minute. The problem is that the other person is psychologically not prepared to agree. This may well be an unconscious reaction to being pressed too hard to do something that he knows, in the end, he will agree to do. But undue or ill-timed pressure may cause him to rethink, and often change his mind.