The authors' research focuses on the mechanisms by which people segregate their general theories about their predictions (i.e., that they are usually unrealistic) from their specific expectations for an upcoming task. This chapter begins by documenting the ubiquity of optimistic predictions in everyday tasks. Topics discussed in this chapter include the following: a cognitive model of the planning fallacy, examining cognitive processes, the generality of the planning fallacy, motivation and the planning fallacy, and debiasing the planning fallacy.