In two brief epigrams, why Sartre had such a hard time in Critique of Dialectical Reason trying to reconcile his existentialism with Marxism:
“It is not the consciousness of men that determines their being, but, on the contrary, their social being that determines their consciousness.”
~ Karl Marx, Preface to A Contribution to the Critique of Political Economy (1859)
“Freedom is existence, and in it existence precedes essence.”
~ Jean-Paul Sartre, “Existentialism Is a Humanism” (1946)
It is a wonder Sartre so hated psychoanalysis and the unconsciousness for the suggestion that freedom was anything other than absolute, but Marxism he could work with.