146 EXECUTING, MONITORING, AND CONTROLLING Leadership skills are essential for project managers be- cause project managers must influence the behavior of others to accomplish project work. In fact, leadership is the predomi- nant contributor to the success of the ad hoc project manager. In small projects, good leadership can succeed even in a cli- mate of otherwise unskilled management. In project management's comparatively brief history, there has been a clear shift in the relative importance of different skills for project manager success. We see that when selecting project managers, the leadership component is of significant value and that its relative importance is on the rise (see Figure 12-1). A project manager has three major leadership roles (see Figure 12-2): communicate, motivate, and solve problems. Communicate