 labor is external to the worker, i.e., it does not belong to his essential being; … in his work, therefore, he does not affirm himself but denies himself, does not feel content but unhappy, does not develop freely his physical and mental energy but mortifies his body and ruins his mind. … It is therefore not the satisfaction of a need; it is merely a means to satisfy needs external to it. (Marx 1844 [1978a: 74])