Four studies investigated the prefactual (alternative preoutcome predictions) and counterfactual (alternative postoutcome ''what might have beens'') mental simulations of defensive pessimists and optimists. In Study 1, defensive pessimists engaged in upward (better than expected) prefactual thinking, whereas optimists engaged in downward (worse than actuality) counterfactual thinking in reaction to a course exam. In Study 2, defensive pessimists preferred upward prefactual thinking and optimists preferred no prefactual thinking when prefactual thoughts were directly manipulated. In Studies 3 and 4, defensive pessimists and optimists differed in reactions to manipulated success and failure, and these reactions were further moderated by the opportunity to engage in prefactual thinking and the possibility of a second try. Individual differences in strategies of prefactual and counterfactual thinking are discussed.