For decades, legal formalism has held that judicial sentencing decisions should be guided by facts, not subjective variables. However, scholars and legal practitioners have long been aware of the influence of psychological factors on legal decisionmaking. In the present quantitative study (N=180), we have examined a model that suggests that belief in malleability (a belief that people’s personalities change and develop) is correlated with perceived severity of the defendant's behavior. We have also examined whether this relationship is mediated by negative and positive emotions. Our analysis revealed that believing in malleability reduces the likelihood of viewing the defendant’s traits as fixed, which leads to more compassionate legal assessment. In addition, our results indicate that the mechanism underlying the relationship between a belief in malleability and judicial assessment is emotional. We discuss the theoretical and practical implications of our findings with an eye on the literature of law and psychology, and implicit beliefs.