What problems do managers face in conducting a global Five Forces analysis?

Global Five force model is a model that is used by managers to conduct a competitive analysis base on five market forces i.e. bargaining power of suppliers, treat of new entrants, threat of substitutes, and bargaining power of buyers and power of the rivals (Porter, 2008). The model does come with some short comings when it is applied by managers in real world situations. For example the managers might be forced by this model to focus on external factors affecting the business an utterly ignore the internal forces. Also the managers may only be able to use this model in their analysis of simple business environment. The fact that the model is really simplistic limits is usability in a complex business environment.