While handling a negotiation, the most important thing to remember is that you are talking to a person who believes he has an equal right to opinion and an equal right to present his points. While you might be thoroughly prepared and be backed with facts, there will often be situations where the other person will choose to disagree with what you are saying for numerous reasons.
Some of them could be his own long-held beliefs, unwillingness to change or adapt, or simply the fact that he feels threatened in the presence of someone who is intellectually superior and refuses this fact to dominate his thought.
We can never know what factors influence a person toward denying certain things that are clearly right or accepting certain things that don’t make any sense, but fighting with them and always trying to be right is a very poor approach towards knowing. Instead of trying to sound and appear right at all times by trying to rain facts and figures, it is a great idea to ask him to present his points and contribute to the discussion so that he feels that he is also bringing equal weight to the table.
There are times when we just have to concede a point or two, just so that the conversation, and subsequently the deal, does not fall through. It is no way being implied that you have to compromise on important points, but the very nature of a negotiation is to see that both sides win. When situations like these come, it is better to give in to a few changes, as compared to giving up on the deal altogether.