No, the best possible negotiation outcome is a win-win, but not just any win-win, but an outcome that results in both parties being completely happy with the outcome. Notice I did not state that the best negotiation results in both parties "getting everything each party wants," but being completely happy with the outcome. Sometimes the parties can do "worse" than the position they may have taken at the outset of a negotiation yet come to change their minds about that position such that they reach agreement on different terms. 

Is it realistic to expect all (or even most) negotiations to result in both parties being completely happy with the outcome? No, not even close. But it can be done when the parties to the negotiation are willing and invested in  results in which both/all parties are completely happy with the outcome.