Mentally contrasting a desired future with present reality is a self-regulation strategy that leads to goal commitment in line with a person's expectations of success. One possible mediator variable of these effects is level of energization. In Study 1, energization assessed by physiological measures was found to mediate the effect of mental contrasting on goal commitment. In Study 2, feelings of energization, as assessed by self-report, mediated the effect of mental contrasting on goal commitment as gauged by performance on an acute stress paradigm (giving a talk in front of a camera). Results imply that when expectations of success are high, mental contrasting provides the level of energy needed to commit to realizing desired futures.