Research in Critical Success Factors (CSFs) of Enterprise Systems (ES) projects has identified numerous practitioner governance mechanisms for ensuring project success. However, such research has not developed a theory of why certain critical success factors encourage project success. Our research develops such theory on a case study where even though the levels of several critical success factors were weak, the project nevertheless succeeded. Specifically, the logistics ES project succeeded even though there was (1) only marginal top management support, (2) low key user commitment, and (3) change management, training and other critical aspects of user management and communication were not well done. Using a modified dialectical lens, we highlight that project team legitimacy appears to be the underlying CSF, and many heretofore identified CSFs are really manifestations of project team legitimacy.