Social proof. A majority of people who believe X in their social circle. Unfortunately thats kind of a chicken and egg problem :P Or, get the majority to belie

Social proof. A majority of people who believe X in their social circle. Unfortunately thats kind of a chicken and egg problem :P Or, get the majority to believe/trust one person on other grounds. Then he/she can convince them together and social proof stays intact if most of them accept most of the message. Sometimes the authority is an institution instead of a person like science, religion, nationalism.