Positive thinking is often assumed to foster effort and success. Research has shown, however, that positive thinking in the form of fantasies about achieving an idealised future predicts less (not more) effort and success and more (not less) depressive symptoms over time. This relationship was mediated by people having invested little effort and achieved little success. Here, we ask a different question. We investigate the emotional consequences of positive fantasies about futures that people cannot act on. Specifically, we analyse these consequences when the future fantasies fail to come true (one’s favourite soccer team loses). Study 1 provided correlational evidence. The more positively soccer fans fantasised about their favourite team winning an upcoming match, the stronger were their negative emotions when their team lost. That is, the more sad, disappointed, and frustrated they felt. Study 2 provided experimental evidence. Soccer fans who were led to fantasise positively about their team winning an upcoming match reported feeling stronger negative emotions after their team lost than those who were led to fantasise negatively. Positive fantasies were not related to how positive participants felt after their team won (joy, happiness, relief). We discuss theoretical and applied implications for emotion regulation in everyday life.