"Being called" refers to the experience of the natural initiation of a Shaman who is “called” to a vocation by the gods.
This initiation of the Shaman occurs after a long period of preparation including much study. Certain characteristics of a future Shaman often include tendencies to nervous disorders and illnesses which are the "signs of election." Also an accident such as a fall, a blow on the head, or being hit by lightning can be a sign of election. However, being "called" and "choosing" are different. "Many are called; few choose to respond." Choosing to respond involves a long process of struggle; pain and suffering which results in the death of the ego while striving for rebirth as the Shaman - he whose head has been purified.
Carlos Castaneda differentiates between the true Shaman and others who seek magical power without having been called spontaneously. Those who seek to obtain powers for their own advantage become Dark Shamans or Sorcerers. The true Shaman or Warrior is one who practices to be Free.