The idea of win-win outcomes is seductive, it implies that everybody gets what they want. This belief can harm you for three reasons:

1.  You cannot know what a win means for the other party. After all, negotiation 101 teaches us that one should never reveal their goals to the other person.
2. Life is not a zero sum game, but neither does it provide unlimited resources. You are competing for the same resources.
3. This only works if the other person is playing the same game, otherwise you will get slaughtered.

Better to aim for “satisfied – satisfied.” More realistic.