When Hester comes back to seeing the marketplace, why does she feel that "those were her realities,-all else had vanished"?

Hester looks out over the crowd and realizes for the first time that her life condemns her to be alone. She looks at her daughter and then fingers the scarlet letter that will remain a part of her from now on. At the thought of her future, she squeezes her daughter so hard that the child cries out in pain. She knows that this is her reality and her main goal in life is to look after and protect Pearl.