Something I've noticed is when other actors are cast in movies along with Duvall most seem to do a much better job in their roles and some even just become better actors altogether.
Even a dumbass like Costner can't kill a DuVall performance.
Now that you mention it, Duvall acting alongside Costner In Open Trails I think Costner did a bang-up job in his role in that movie and become a better actor since solely BECAUSE of Duvall's influence.
