Therese’s lips opened to speak, but her mind was too far away. Her mind was at a distant point, at a distant vortex that opened on the scene in the dimly lighted, terrifying room where the two of them seemed in desperate combat. And at the point of the vortex where her mind was, she knew it was the hopelessness that terrified her and nothing else. It was the hopelessness of Mrs. Robichek’s ailing body and her job at the store, of her stack of dresses in the trunk, of her ugliness, the hopelessness of which the end of her life was entirely composed. And the hopelessness of herself, of ever being the person she wanted to be and of doing the things that person would do. Had all her life been nothing but a dream, and was this real? It was the terror of this hopelessness that made her want to shed the dress and flee before it was too late, before the chains fell around her and locked.
Existential dread has more meaning to it when there is an actual fear behind it. The fear described by Highsmith has more meaning that the fear described by, for instance, Camus.
When your existence is fraught and denied you can better understand existence.