Expectancy theory is based on the subjective probability (expectancy) and projected value (valence). Based on this notion, an individual chooses his or her behaviors based on the interaction between the valences perceived to be associated with the outcomes, and the appraisal of the probability of that behavior resulting in those outcomes. Expectancies have been found to be predictive of many outcomes, such as treatment outcomes, behavioral change, and training reactions. The goal of the present study is to empirically investigate this issue within the mental health field. While virtual reality appears to be a promising preventative technique for posttraumatic stress disorder, the literature has not yet accounted for expectations and their influence on reactions. More specifically, it is unknown how expectancies influence reactions. Therefore, this study examines videogame self-efficacy as a mechanism through which expectations influence reactions. In the present study 60 participants completed an expectancy scale, VGSE scale, played a serious game designed to prepare soldiers for the psychological challenges associated with deployment, and completed a reactions survey. A mediation analysis was conducted to examine if videogame self-efficacy is a mechanism through which expectations predict reactions. Analyses revealed that videogame self-efficacy partially mediated the relationship between expectancies and reactions.