This article is a contribution to the continuing discussion on the validity of basic theoretical currents which explain the issues of creating sustainable competitive advantage (SCA). The article adopts a thesis on complementarity of two basic approaches (external analysis and internal analysis) and attempts to determine situations in which each of them is more appropriate. The starting point of the analysis is a short characteristics of these approaches pointing out their drawbacks. In the case of the Porter approach this is an inadequate explanation of sustaining the advantage, while in the case of the resource approach this is the issue of gaining a leading position on the market of resources. Then, the process of gaining SCA was presented on example of commercial companies (Ikea, Benetton and Wal-Mart), by the same token illustrating the main thesis, of the article. In conclusion of these considerations it was argued that although the internal analysis currently plays a major role in formulating the strategy of commercial companies, due to the turmoiled environment of that sector and, primarily, frequent changes in consumer preferences and intensive competition, organizations are sometimes forced to develop in directions indicated by the eternal analysis current, although this may even mean a fall in short term profitability.