The message is clear: Project leaders must adapt to their circumstances or they will fail. This circumstance is especially evident when applying the appropriate leadership style under a given situation, e.g., during a particular phase. From Fiedler's contingency theory and Hersey and Blanchard's leadership model to Kliem and Anderson's organizational engineering, for example, the appropriate leadership style can make a difference.
Adaptability involves others factors as well. Project leaders must be adaptable to new circumstances due to market changes; they must adapt to changing membership among stakeholders; and they must adapt to new tools, techniques, and methodologies. They must also anticipate such changes and respond through effective change management.
Their response must be more than mechanical. They must adapt in such a way that encourages and helps stakeholders to adapt also. Otherwise, project managers will experience resistance to change both on a personal level and stakeholder level. Resistance will occur and a project will fail.