As one of the core topics in strategic group research, considerable research has been conducted on the relationship between strategic groups and performance. Most studies have tested performance differences across strategic groups under the premise that strategy significantly affects performance, yet inconsistencies in research findings persist. Above all, by focusing exclusively on empirical research without systematic research models, researchers' arbitrary inferences have pervaded the interpretation of results, creating significant problems in terms of theoretical advancement through the accumulation of research findings. Accordingly, this study, based on the recently emerging resource-based view, systematically identified the reasons for the absence of performance differences across strategic groups from the perspective that firms' hard-to-imitate internal capabilities are the source of competitive advantage. Specifically, by demonstrating that performance differences exist among firms within the same strategic group, this study supported the proposition that performance differences do not exist across strategic groups, and further empirically proved that there are significant performance differences according to firms' internal capabilities. These results empirically support the validity of the resource-based view. In light of these findings, a shift in research focus is called for if strategic group research is to contribute to theory building in the field of strategic management. That is, rather than simply examining the relationship between strategic groups and performance, longitudinal studies on the dynamic changes of strategic groups—capturing the formation and mobility paths of strategic groups and identifying their causes—are needed. Furthermore, for the recently proposed resource-based view to be established as a theory of the firm or strategy, a more rigorous definition of the concept of resource capabilities and consensus on analytical frameworks must be achieved first.