We examine bilateral bargaining, where participants first select a preferred allocation norm among equal division, equal gain, and proportional division. When matched with another sharing the same norm, participants decide whether to adhere to the projected division or negotiate a different outcome. Experimental results reveal that norm abandonment occurs more frequently when allocations are perceived as unfair: high contributors in equal division and low contributors in proportional division. Attachment is sturdiest for strict equality and weakest for proportionality. Equal gain, a middle ground, is the most favored at both preselection and negotiation outcomes. Several applications in international conflicts are discussed.