Negotiations are ubiquitous in business, politics, and private life. In many cases their outcome is of great importance. Yet, negotiators frequently act irrationally and fail to reach mutually beneficial agreements. Cognitive biases like overconfidence, egocentrism, and the mythical fixed pie illusion oftentimes foreclose profitable results. A further cognitive bias is the attachment effect: Parties are influenced by their subjective expectations formed on account of the exchange of offers, they form reference points, and loss aversion potentially leads to a change of preferences when...