2. _As different periods of time must elapse before services are enjoyed, the expected value of all products but those immediately available is discounted in advance._ The services that afford gratification immediately, and those that afford gratification at a later time, are judged and compared at one and the same moment. All economic life centers in the present. This difference in the time of services surely cannot be ignored. If Robinson Crusoe, at work on his island with his limited supply of energy, continues to provide for next year's enjoyment, neglecting the present, present goods become scarce and their utility rises as compared with the future goods the same labor secures. To escape inconvenience, and in the extremest case to escape starvation, Crusoe would be compelled to restore the equilibrium between the wants of the two periods by shifting his labor back to the present. So in each little economic group and in our complex society there is constant rivalry of present and future wants, competing for the limited present supply of labor. The present says, "Give me your labor and I will give you the fullest enjoyment." The future says, "I will give you a greater gratification, but you must wait for it." A given labor force thus making possible a wide range of choice among present and future services, labor is distributed according to the prevailing rate of time-value, which, as we have seen, is approximately expressed by the rate of interest. If the rate of interest is high, it means that the present is urgent and will not easily yield to the future. If the rate is low, it implies that the present is comparatively well provided for, and that future wants are given more consideration. [Sidenote: The employer adjusts his labor force to the interest rate]