Directors like Satyajit Ray, Rossellini, Bresson, Buñuel, Forman, Scorsese, and Spike Lee have used non-professional actors precisely in order that the people we see on the screen may be scarcely more explained than reality itself. Professionals, except fo the greatest, usually play not just the necessary role, but an explanation of the role.
John Berger (2014). “Selected Essays of John Berger”, p.480, Bloomsbury Publishing