In a classic New Yorker cartoon, a dinner guest shows up for the party, hands the host a $20 bill, and announce that this was the amount he had planned to spend on a bottle of win before he ran out of time. Negotiation buffs might admire the guest for making an efficient tradeoff that saved him the effort of shopping and gave the host $20 to spend as he wished. But most people would view the guest’s behavior as highly inappropriate. Why?