Sartre's concept of freedom is unique: freedom is the condition of the pour-soi; and since the pour-soi exists as "lack," its freedom is the expression of its Nothingness. The pour-soi is what it is not, and is not what it is. This instability defines its freedom. Again, since this is the condition of the pour-soi, man is condemned to his freedom. Man is condemned to be free because man class="EmphasisTypeItalic ">is freedom.