According to Purcell (2001), this theory is limited by the impossibility of modeling all the contingent variables, the difficult of showing their interconnection, and the way in which changes in one variable have an impact on others. Boxall and Purcell (2003) further emphasize the complexity of matching HR and business strategy by stating the need to keep up with ongoing environmental change. They bring attention to a model by Wright (2005) asserting that SHRM should simultaneously promote fit and flexibility to cope with the future. However, responding to those external demands may undermine the possibility of achieving internal fit (Legge, 2005). Models of external fit fail to recognize the needs of employees. More evident in highly competitive markets, businesses cannot survive without balancing the pressures from social norms, labour laws and critical employee interests. Conclusively, an alignment of business and employee needs is needed. The best fit school also lacks emphasis on the internal context of individual businesses within the same sector and the unique characteristics and practices that may provide its main source of sustainable competitive advantage.