When are perceivers guided more by implicit social-cognitive theories of personality and when more by trait theories? As perceivers become more familiar with a person they infer relatively more psychological mediating variables (e.g., construals, goals) that underlie the person's behavior and relatively fewer broad, uncontextualized traits such as aggressive or friendly (Study 1). The effects of familiarity are moderated by the importance of the target to perceivers (Study 2). Specifically, perceivers make relatively more inferences using mediating variables and fewer inferences with traits as the target becomes more familiar, if and only if the target plays an important role in their lives. The findings indicate that psychological mediating variables play a significant role in lay perceptions of people and specify conditions in which perceiver's function like implicit social-cognitive theorists, namely, when the perceived is familiar and important to the perceiver.