We examined the extent to which cognitive ability, Conscientiousness, and Openness to Experience predict decision-making performance prior to and after unforeseen changes in the task context. Seventy-three undergraduates made decisions on a series of 75 problems during a 3-hour computerized simulation. Unbeknownst to participants, the rules used in determining correct decisions changed after problems 25 and 50. Effects of the individual differences on decision-making performance became significantly stronger after the changes. Only cognitive ability explained variance in prechange performance. Individuals with higher cognitive ability made better decisions. After the change, the cognitive ability effect increased and the effects of Conscientiousness and Openness became statistically significant. As expected, those with high Openness made better decisions. Unexpectedly, those with low Conscientiousness made better decisions. Subsequent analyses revealed that this surprising effect for Conscientiousness was due to the traits reflecting dependability (i.e., order, dutiful-ness, deliberation) rather than volition (i.e., competence, achievement striving, self-discipline).