The literature exploring other regarding behavior sheds important light on interesting social phenomena, yet less attention has been given to how the received results speak to foundational assumptions within economics. Our study synthesizes the empirical evidence, showing that recent work challenges convex preference theory but is largely consistent with rational choice theory. Guided by this understanding, we design a new, more demanding test of a central tenet of economics—the contraction axiom—within a sharing framework. Making use of more than 325 dictators participating in a series of allocation games, we show that sharing choices violate the contraction axiom. We advance a new theory that augments standard models with moral reference points to explain our experimental data. Our theory also organizes the broader sharing patterns in the received literature