 Like other animals, humans give more weight to present satisfaction than to future satisfaction. In other words, we discount future utility. Insofar as one discounts future utility, one prefers, other things equal, to get a reward sooner rather than later; relatedly, the closer one gets to a future reward, the more the reward is valued. If we map the value (to a particular agent) of a given future reward as a function of time, we get a discount curve, such as in Figure 1: