这道题应该是前面高手说的关于sunk costs的。sunk costs在做决定的时候是不用考虑的。计算npv就知道最多投资多少了。cost和产出量的关系似乎不明确,所以很难计算marginal cost. 同样也不好算marginal revenue.
当然这是传统经济学的论点。维基百科提到: ``In economics and business decision-making, sunk costs are retrospective (past) costs that have already been incurred and cannot be recovered. Sunk costs are sometimes contrasted with prospective costs, which are future costs that may be incurred or changed if an action is taken. Both retrospective and prospective costs may be either fixed (that is, they are not dependent on the volume of economic activity, however measured) or variable (dependent on volume).
In traditional microeconomic theory, only prospective (future) costs are relevant to an investment decision. Traditional economics proposes that an economic actor not let sunk costs influence one's decisions, because doing so would not be rationally assessing a decision exclusively on its own merits. The decision-maker may make rational decisions according to their own incentives; these incentives may dictate different decisions than would be dictated by efficiency or profitability, and this is considered an incentive problem and distinct from a sunk cost problem.
Evidence from behavioral economics suggests this theory fails to predict real-world behavior. Sunk costs greatly affect actors' decisions, because many humans are loss-averse and thus normally act irrationally when making economic decisions.''
行为经济学认为sunk costs是有影响的。