"There should not be tension in negotiation".
Is this affirmation true?

Wrong; tension is normal and even necessary in negotiation.

Each party must indeed defend the satisfaction of his interests. This naturally creates a tension between the participants that will encourage them to be creative in finding solutions rich and satisfying for both parties.

A negotiation with very little or no tension often leads to poor agreements for both parties.                

However, we must do everything to avoid creating tension in relational.                

We can be respectful of his interlocutor while remaining firm on the satisfaction of our major interests.