Overcoming the planning fallacy through willpower : effects of implementation intentions on actual and predicted task-completion times

Previous work has shown that people often underestimate their task-completion times (Buehler, Griffin, & Ross, 1994). The present research examined whether this optimistic bias may be reduced through the formation of implementation intentions. In an experimental study, participants were requested to complete an assignment within a specified time period. Half of these participants made implementation intentions about where and when they would complete the assignment. The remaining participants were simply given the goal of completing the assignment. The results showed that furnishing participants' goals with implementation intentions led to (a) more optimistic completion predictions, (b) an even greater increase in actual rates of goal completion, and, consequently, (c) a significant reduction in optimistic bias in completion predictions. Furthermore, the reduction in optimistic bias among implementation–intention participants was found to be mediated by a smaller number of interruptions while working on the assignment. Together, these findings attest to the importance of implementation planning in overcoming unrealistic optimism in task-completion predictions. Copyright © 2000 John Wiley & Sons, Ltd.

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