The current review synthesizes and builds from the extant literature to help explain how and why conscientiousness predicts a vast array of positive life outcomes. Toward this end, we present the Invest-and-Accrue model of conscientiousness, which describes conscientiousness as a disposition toward “investing” in ways that allow for future success. The value of this model is made apparent in its applicability across different life domains, as well as its potential for describing how individuals can change on conscientiousness throughout the life span. Moreover, the model can help explain why conscientiousness is relatively unique from other Big Five traits in its ability to predict positive life outcomes seemingly in any domain. In sum, this model should prove valuable for researchers across psychological disciplines, by providing an organizing framework from which to make connections across findings in personality, social, developmental, organizational, and educational psychology.