I have watch this documentary twice and I believe it is a good one. Shelby Lee Adams tell us that photographers should shoot things that they know. If you don't know what you are shooting you will not be able to get good images as someone that does know. Adams grew up in the Appalachia area. He knows the people there, their living style, and he understands them. He really shows it in his photographs. He places his subject in ever photograph. Adams respects everyone of his subjects that he will not publish the photograph if they don't like it.
A lot of people in Adams work do not smile. They look like that subjects are unhappy with who they are and that they are living a cruel life. But Adams explains that is not his intentions. He is shoot the for who they are, not what they are.