It is not a profession that one chooses, it is fate which calls a person to be a shaman.
To practice shamanism doesn't mean "being" a shaman. One speaks of a “shaman” only if it is a person who has been trained in the indigenous environment in the traditional methods of shamanism, which are specific to certain indigenous tribes and cultures, and who has been initiated into this profession.
Even within a tribal cultur a powerful healer would never call himself a shaman. With dedication and without ulterior motives he wants to help humans. It is the community which gives him this "title".
Shamans don't "believe", they "know" because of their immediate experience.