"Somehow I think it was declared very early on that I was the - if not the black sheep of the family, not a very good student"

Dustin Hoffman's quote implies that he was not accepted by his family and was not viewed as an effective trainee. This might be due to his lack of scholastic success or his rebellious nature. It is possible that his family had high expectations for him, but he was not able to meet them. This could have triggered tension between him and his family, leading to him being seen as the "black sheep" of the family. It is also possible that his household was not encouraging of his profession options, which might have additional strained their relationship. Whatever the factor, it is clear that Dustin Hoffman seemed like he was not accepted by his household and was not seen as an effective trainee.