How might people best persuade themselves to engage in beneficial activities, such as dieting, exercise, and studying? One strategy is to think about actions. Another strategy is to think about reasons. In previous research, students who were directed to think about actions increased their study intentions more than did students who were directed to think about reasons. The present experiment tested whether thinking about actions was effective because of idea generation (coming up with the thoughts) or because of mental simulation (imagining the scenarios). In immediate and delayed measures, directed thinking about actions (but not reasons) proved generally more effective when students focused on mental simulation than when they focused on idea generation. Theoretical and applied implications are discussed.