The marginal disutility of labor increases as a worker expends more units of labor, since clearly those units that have less disutility will be expended most readily. This conclusion is easier to understand if one recognizes that a principal component of the disutility of labor is the time that the worker must relinquish. As a worker contributes more and more hours of labor, he or she must relinquish time that might have been devoted to more and more urgent alternative uses.