What does this mean? And how does this emphasis upon the fundamental character of non being lead to an interpretation of the experience of anxiety and of the need for an existential courage?

In The Courage to Be Tillich begins by emphasizing that non being belongs to being. What does this mean?

And how does this emphasis upon the fundamental character of non being lead to an interpretation of the experience of anxiety and of the need for an existential courage?

We also find an emphasis upon non being in Beauvoir’s account of existential ethics. Does this mean that Beauvoir in her own way elaborates an existential courage, a courage to be? explain.