BATNA stands for Best Alternative To No Agreement. It is what you are going to do if the agreement on the subject is impossible.
It is evident that better BATNA means a stronger position in the negotiations. You just care less whether you will reach the agreement and can live with the consequences of not achieving it.
Otherwise, you should know how to manage the desire to reach the necessary agreement, or it will spoil the fun. Richard Gere’s character in “Arbitrage” movie has been running the negotiations to sell his company for $0,5b. His BATNA was 20 years in jail for the felony. He was bluffing and managed to sell it for $0,42b.