Investigated the influence of counterfactual reasoning on accuracy when predicting the outcomes of future personal events. 260 graduate business students made predictions about the results of their job search efforts 9 mo away (e.g., starting salary); all of the events involved positive outcomes, in which unrealistic optimism was expected. These events were constructed to vary in their underlying base rate of occurrence. Some Ss generated pro and/or con reasons concerning event occurrence before making their predictions. At low- to moderate-base rates, predictive accuracy increased when Ss generated a con reason. However, at high-base rates (events that occurred for a majority of the Ss), con reason generation had no effect on accuracy—all Ss were more accurate in predicting these events. Generation of pro reasons had no effect on accuracy, suggesting that Ss may have automatically generated supportive reasons as a by-product of the question-answering process. A substantive analysis of the reasons indicated that Ss attributed pro reasons to internal factors and con reasons to external factors. Moreover, Ss who generated internal pro reasons were less accurate than Ss generating external pro or either type of con reason.