It is meant to convey a sense of the single-pointed emphasis of existentialism on the here and now. Simone is partially visible to his side. This question is way beyond the scope of this page or any of the more ambitious pages I have links for.
Existentialism chooses to look at issues that traditional philosophy ignored.
It is often criticised as gutter philosophy. For most existentialists life is hard work. It requires strength to confront the infinite wall of choices that face us in every instant. I'm free to choose for myself what my life is like. They refuse to recognize that at every second of every day there are millions of choices they could make.