From an excellent book I highly recommend, The Areas of My Expertise by John Hodgman (no relation to the Tasmanian political dynasty).
SECRETS OF SUCCESSFUL NEGOTIATION [no. 4/5]
A bestselling author on the subject of “negotiation” reminds: “Negotiation requires compromise. Each party must gain something, and each must give something up. Before you begin your negotiation, privately consider what you are willing to give away. Now gather all of that material together and put it in a sack. Hide the sack in a secure location, such as a cave that is laced with explosives that you can detonate by remote control. Take the remote control in with you to the negotiation. As any experienced negotiator knows, in order to succeed, you must be willing to walk away from the deal at any moment, and then blow up the cave. Note: The sack should be made of velvet.”