The present study sought to test a cognitive capacity explanation of the distraction-conflict theory of social facilitation (Baron, 1986). Introverts and extraverts performed a sustained attention to response task and a word-pair task. Participants performed these tasks in the presence of social distractions (coactor and evaluator) and non-social distractions (low and high complexity music) to determine if performance in the difference conditions was moderated by extraversion. In addition, this study proposed that the mediators of the moderated relationship between condition and extraversion would be boredom and mind-wandering. Results indicate that extraverts need more outside stimulation to achieve performance facilitation than introverts. Introverts, on the other hand, showed performance impairment when over stimulated. When performance was facilitated, the amount of task unrelated thoughts decreased, whereas when performance was impaired, task unrelated thoughts increased. Theses results support a cognitive capacity explanation for the distraction-conflict theory of social facilitation.