To be a source of sustained competitive advantage, resources controlled by a firm must be valuable—in that they can be used to reduce a firm’s costs and/or used to increase the willingness of customers to pay—rare among competing firms, costly for other firms to imitate, and not have any functionally equivalent substitutes. Resources are most likely to be costly to imitate and non-substitutable when they are socially complex (e.g., organizational culture), developed over long periods of time (i.e., are path dependent), and when actions needed to develop these resources are not obvious (i.e., they are causally ambiguous)
