What are the assumptions that a communicative framework for negotiation is based on and how can this information be useful to a negotiator in bargaining for a successful outcome?

In their search for solutions that meet the objectives and needs of both sides, negotiators must be both firm and flexible. This statement seems to be contradictory; however, it is a valid statement. Explain what this means in the context of negotiations and describe an example where a negotiator can be both firm and flexible.

What are the assumptions that a communicative framework for negotiation is based on and how can this information be useful to a negotiator in bargaining for a successful outcome?