When you’re in the middle of an important negotiation, validating the other person's point is not typically the first thing on your mind. It's more likely that you are thinking about what you want. But considering the other person's point should actually be your top priority. If you validate your counterpart’s perspective, expertise, and feelings, you will be positioned to achieve the best outcome for yourself.
The opposing-parties approach of you vs. them is no longer valid. Today that approach must be replaced by the business partners approach to negotiation. Openness and sincerity replace being self-centered and egotistical. Show the other person, who is now your partner in negotiation, that you value their perspective and needs.
The likely result of taking a me-only position will limit your ability to reach an amicable agreement. You may reach an impasse. The impasse is the point within a negotiation when the 2 parties are unable to see an effective agreement. As this develops, each person in the negotiation might dig their heels in deeper, anchoring themselves in their own position without compromise or a path to completing the negotiation.
The negotiation itself should be a careful evaluation 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. In an ideal situation, you will find that the other person wants what you are prepared to give, and that you are prepared to give what the other person wants. For a negotiation outcome to be positive, both parties should feel positive about the negotiation once it's over.
When you don't expect to deal with the other person ever again, or you do not need their goodwill in the future, then it may be appropriate to seek to win a negotiation while the other party loses out. However, doing so with someone with whom you have an ongoing relationship will damage that relationship and may lead to reprisals later. Instead, fairness, honesty and openness are the best policies. Considering the perspective of the other has the best chance to yield a positive negotiation result. In addition, this helps people keep good working relationships afterwards.