 Research in experimental psychology (see, for example, Kirby &amp; Herrnstein 1995, Millar &amp; Navarick 1984, Solnick et al. 1980, and Ainslie 2001) suggests that, given how animals, including humans, discount future utility, there are plenty of cases in which the discount curves from two rewards, one a small reward and the other a larger later reward, cross, as in Figure 2: