What is the theme in The Way of the Shaman by Michael Harner?

Personal power is another theme in the book. One of the primary aspects of shamanism is the acquisition, maintenance, and transference of power. Acquiring power requires discipline, discomfort, and a willingness to suspend belief in only what one can perceive using the normal senses. Sometimes it requires the use of mind-altering drugs, stressful conditions that challenge the precepts of normal reality, or solitude.