Arthur Miller's Death of a Salesman is packed full of memorable quotes, many of which are vital to the full understanding of the play and its themes. This answer will show two examples.
LINDA: Willy, dear. Talk to them again. There’s no reason why you can’t work in New York.
WILLY: They don’t need me in New York. I’m the New England man. I’m vital in New England. (Act 1)
In the beginning, Willy is still focused on his worth as a salesman in New England. However, he is not thinking long-term, nor is he thinking about how he is actually failing in his job. Instead, he is holding on to a rose-colored memory of his best years and refusing to recognize that his successes as a salesman are behind him. Had he considered moving his operations to New York, he might have found new self-worth in a useful position.
WILLY: I've got to get some seeds. I've got to get some seeds, right away. Nothing’s planted. I don’t have a thing in the ground.
Here, near the end of the play, Willy is still refusing to recognize his failure as a salesman and as a father, and yet inside he knows that he is not leaving anything of worth behind. He has "nothing planted," either in his family or as a legacy. He knows that it is still possible to leave some sort of positive mark, but he cannot understand what, or how.