According to historian Steven Stoll, it's this:
"Charismatic leaders often depend on dedicated interpreters. Charisma is not the ability to communicate, and it is certainly not the quality of being well liked. It is the capacity to impose an idea on others that they internalize. Charismatic leaders make people see the world as they do--but not always by making reasoned arguments. They foretell obscurely, speak in poetry, and declare irreducible truths without evidence. They don't have friends, since everyone serves the instrumental purpose of advancing their views. So Aaron spoke for his brother Moses and performed the rituals that translated prophecy into religious practice. Jesus needed the disciples to elaborate and spread his message. Sherlock Holmes depended on Dr. Watson to act as a catalyst for his thinking about crime."
Steven Stoll, The Great Delusion, Hill and Wang, NY, NY, 2008, pg. 97.