But if the capitalist builds upon this distinctive quality and potential of human labor power, it is also this quality, by its very indeterminacy, which place before him his greatest challenge and problem.  The coin of labor has its obverse side: in purchasing labor power that can do much, he is at the same time purchasing an undefined quality and quantity.  What he buys is infinite in potential, but in its realization it is limited by the subjective state of the workers, by their previous history, by the general social conditions under which they work as well as the particular conditions of the enterprise, and by the technical setting of their labor.  The work actually performed will be affected by these and many other factors, including the organization of the process and forms of supervision over it, if any (39).

It thus becomes essential for the capitalist that control over the labor process pass from the hands of the worker to his own.  This transition presents itself in history as the progressive alienation of the process of production from the worker; to the capitalist, it presents itself as the problem of management (39-40).