In the preceding chapter, we examined some of the evidence regarding the ways in which people judge probabilities, and the sometimes intense debate this evidence has provoked. Judging probabilities may be interesting in itself, but it attracts extra interest because it has for a long time been acknowledged as central to a central human activity: making decisions. Thus, it may be interesting to see how people figure out whether someone will be in a certain place, or whether it will rain today, or what the odds are in a lottery, but it is even more interesting to see how they decide whether to go into the bar, cancel a picnic, or buy a ticket. Decision making thus fundamentally concerns combining information about probability with information about desires and interests: how much do you want to meet her, how important is the picnic, how much is the prize worth?