People tend to overestimate their comparative likelihood of experiencing a rosy future. The present research suggests that one reason for this error is that when people compare their likelihood of experiencing an event with that of the average person, they focus on their own chances of experiencing the event and insufficiently consider the likelihood of the average person experiencing the event. As a consequence, people tend to think that they are more likely than the average person to experience common events and less likely than the average person to experience rare events. This causes unrealistic optimism in the case of common desirable events and rare undesirable events, but unrealistic pessimism in the case of rare desirable events and common undesirable events (Studies 1 and 2). Study 2 further suggests that both egocentrism and focalism underlie these biases. These results suggest that unrealistic optimism is not as ubiquitous as once thought.