Sometimes a belief doesn’t change but still gets Persona. “I must deliver the MacGuffun!” gets Persona when it’s done, and then it’s time for a new belief. “I must protect the MacGuffin!” could get Persona when it has been dramatically protected at the climax of a storyline, but the character may still have that belief as a priority. They get the artha and they’re telling the GM that they still want the MacGuffin front and center in the character’s universe.