A negotiation changes when you know what happens if no agreement is reached.

The whole shape of a negotiation is set by what happens if it fails. Knowing your fallback precisely, not vaguely, tells you what you can accept, what you can refuse, and when to stop, and it removes most of the anxiety from the room. Without it, you are guessing, and guessing tends to make people accept whatever is in front of them. The alternative is the real source of composure.

Before any significant negotiation, write down exactly what you will do if there is no agreement. Make it specific enough to act on. That single page changes how the conversation feels from the first minute.