The present paper's goal was to investigate the mechanisms that relate personality to task performance. In particular, we argue that momentary levels of neuroticism (i.e., state neuroticism) are triggered by perceptions of work pressure and task complexity, and that these momentary levels of neuroticism subsequently mediate the relationship between the job demands and momentary task performance. Moreover, we hypothesized that the relationship between job demands and state neuroticism is moderated by trait neuroticism. To test this model, we conducted an event reconstruction study and a day reconstruction study. The results revealed that trait personality indeed moderated the momentary job demands - state neuroticism relationship, and in three out of four cases state neuroticism was found to mediate the relationship between momentary job demands and momentary task performance. From a practical point-of-view our results suggest that employees' task performance can be increased by enhancing the way in which individuals cope with job demands, and that this strategy would be particularly helpful for individuals for whom the job demands - state neuroticism relationship is the strongest (i.e., employees high in trait neuroticism).