i'm reading a short excerpt from C.Wright Mills book The Sociological Imagination, and i have no idea when he writes this: No social study has completed its intellectual journey until it comes back to the problems of biography, of history, and of their intersections?

Question

i'm reading a short excerpt from C.Wright Mills book The Sociological Imagination, and i have no idea when he writes this: No social study has completed its intellectual journey until it comes back to the problems of biography, of history, and of their intersections?
quoted--"No social study that does not come back to the problems of biography, of history and of their intersections within a society has completed its intellectual journey."

please explain this to me
confused :S