only resources that are valuable, rare, inimitable and for which there is no substitute can provide a firm with a sustainable competitive advantage

Impact of top management team on firm performance in small and medium-sized enterprises adopting commercial open-source enterprise resource planning
Sandra J. Cereola a , Benson Wier b & Carolyn Strand Norman b

“only resources that are valuable, rare, inimitable and for which there is no substitute can provide a firm with a sustainable competitive advantage”

from

“Theoretical contributions to resource theory arising out of Penrose (1959) posit that a firm’s internal resources are the primary predictors of superior performance. That is, some resources provide the means to achieve competitive and strategic advantages, while others provide the means to achieve superior long-term financial performance (Wernerfelt 1984, Barney 1991, Kearns and Lederer 2003). However, only resources that are valuable, rare, inimitable and for which there is no substitute can provide a firm with a sustainable competitive advantage (Wernerfelt 1984, Barney 1991). As competitive advantage focuses on the relative success of the firm (Porter 1985), firms need not be large to gain a competitive advantage. SMEs can do so when they are able to take advantage of resources that allow them to create firm-specific resources. That is, SMEs have an equal chance to compete since they have the advantage of greater strength in innovation, flexibility and are adaptive to change (Wicks 2005).”

http://dx.doi.org/10.1080/0144929X.2010.528029