Scio Occultus Res
Names have power in magic. Magical Thinking tells us that, on a mystical level, the name and the thing named are the same. To prevent their enemies from using their names against them, most mages choose a working name to interact with others. This is the Shadow Name, and is usually symbolic of the mage or of something the mage aspires to. It can come from any symbolic tradition, language, body of myth, or ethnicity. The only catch is that, as the mage uses it, it shapes him into the ideal it represents.
Because names have power.