Before approaching situations, individuals frequently imagine "what would happen, if . . . ." Such prefactual thought can promote confidence and facilitate behavior preparation when the upcoming situation can benefit from forethought, but it also delays action. The present research tested how social power predicts prefactual thought when its benefits are clear versus ambiguous. Power enhances flexible behavior adaptation and action tendencies—presumably without much forethought. We therefore proposed that power diminishes prefactual thought, unless the situation suggests that such thought is adaptive (i.e., could benefit performance). Power-holders indeed generated less prefactuals than the powerless (Experiments 1 and 2), but only if benefits for performance were ambiguous rather than clear (Experiment 3). These findings indicate that social context factors related to confidence affect prefactual thought, and that power-holders’ flexible adaptation to the situation sometimes elicits inaction (i.e., prefactual thought) rather than spontaneous action.