The worker becomes all the poorer the more wealth he produces, the more his production increases in power and range. The worker becomes an ever cheaper commodity the more commodities he creates. With the increasing value of the world of things proceeds in direct proportion to the devaluation of the world of men. Labour produces not only commodities; it produces itself and the worker as a commodity -- and does so in the proportion in which it produces commodities generally.
Economic and Philosophic Manuscripts (1844)