In The Second Sex, Beauvoir notes that, historically, men and women have been assigned essential roles. Men have been considered more free and the dominant sex while women have been given the role of men's "Other" meaning that they are defined by their difference from the men as the "norm." Thus, women have been defined as "secondary" to, and "other" than, men. Since the essentialist concepts of men and women, as primary and secondary, are considered like Plato's ideal forms as eternal and unchanging, a woman who acts outside of her role is considered wrong. And since her role requires that she is less free than, and subservient to, man, she can never transcend that role because it is against that essentialist role for her to be transcendent.
Beauvoir argues that the absolute (eternal and unchanging) concept of man's role is that he is the freer of the two genders and therefore man is more able to transcend his role and all aspects of his life. She argues that the absolute Other (woman's role) is based upon immanence which requires that woman's role is given a limited domain.
In fact every existent is at once immanence and transcendence; when one offers the existent no aim, or prevents him from attaining any, or robs him of his victory, then his transcendence falls vainly into the past--that is to say, falls back into immanence. This is the lot assigned to woman in the patriarchate; but it is in no way a vocation, any more than slavery is the vocation of the slave.
Beauvoir notes that men and women are capable of immanence and transcendence. But as long as women are prevented from engaging in roles which utilize transcendence in real life, they will be prevented from becoming something more than that prescribed role as man's "other."
Beauvoir fails to note that choosing to work as a homemaker can be a chosen (and therefore existential and potentially transcendent) vocation. But her overall point is still profound. She suggests that a woman is prescribed (which is antithetical to existentialism, the idea that we are defined by our acts, not prescribed roles) a role and that role is based upon limitations: immanence. She further suggests that men are prescribed a role of transcendence which allows them, by the nature of the definition of transcendence, to have no limitations, physically and mentally.