Whether an act gives rise to liability should turn on its tendency to yield particular outcomes rather than on its ultimate effect, which may have resulted from extraneous factors beyond the actor’s control and foresight. This principle is firmly ingrained in jurisprudence, yet antitrust law violates this principle in a number of unappreciated ways. The law evaluates commercial conduct based not on the nature of the challenged behavior to bring about particular results, but on the stochastic confluence of extraneous factors. This Article explores the phenomenon of extraneous liability in antitrust law, finding fault with several important features of the modern antitrust system. Nevertheless, this Article accepts a legitimate role for extraneous factors in antitrust analysis. To the extent that such forces are both reasonably identifiable and at least somewhat determinate ex ante, they may appropriately affect the legality of conduct, the future commercial impact of which depends on those forces.