Assume and Fail!
The difference between man and beast is that man assumes he is better than the beast. In the wild a man is only a match if he has the right equipment, is well trained, and knows the jungle. A camera on safari is no defense against a charging rhino!
In every dispute resolution one must assume certain things about the other person in order to make progress. As an example, you may be trying to measure when the other person has reached his limit in the discussion before you make your final concession. How you come to this conclusion must be based in part on an assumption on your part.
To assume is to presume or presuppose. Assume also means to imagine. This is dangerous territory in a negotiation. You need to limit your imagination as much as possible by turning to your communication skills and validating your assumptions. But, better still, you need to minimize your assumptions.
Assume less, listen more:
-Identify what you are assuming before a meeting, and when the meeting starts, ask questions to validate your assumptions.
-Seek third party input to validate an assumption. Don't make an assumption about something that can be researched.
-If you don't know, ask. You may be surprised at how open the other person is.
If the assumption is about a significant issue, don't rely on your gut. Investigate, question, brainstorm, network and research until you can assess the approximate accurateness of your assumption. No one said negotiating is easy.