The negotiation itself is a careful exploration of your position and the other person's position, with the goal of finding a mutually acceptable compromise that gives you both as much of what you want as possible. People's positions are rarely as fundamentally opposed as they may initially appear – the other person may have very different goals from the ones you expect!
In an ideal situation, you will find that the other person wants what you are prepared to trade, and that you are prepared to give what the other person wants.
If this is not the case and one person must give way, then it is fair for this person to try to negotiate some form of compensation for doing so – the scale of this compensation will often depend on the many of the factors we discussed above. Ultimately, both sides should feel comfortable with the final solution if the agreement is to be considered win-win.
Only consider win-lose negotiation if you don't need to have an ongoing relationship with the other party as, having lost, they are unlikely to want to work with you again. Equally, you should expect that if they need to fulfill some part of a deal in which you have "won," they may be uncooperative and legalistic about the way they do this.