“The worker is no longer the slave to his reproductive urge. He is a free bargaining agent who enters the market to dispose of the one commodity he commands — labor power — and if he gets a rise in wages he will not be so foolish as to squander it in a self-defeating proliferation of his numbers.
The capitalist faces him in the arena. His greed and lust for wealth are caustically described in those chapters that leave the abstract world for a look into 1860 England. But it is worth noting that he is not money hungry from mere motives of rapacity; he is an owner-entrepreneur engaged in an endless race against his fellow owner-entrepreneurs; he must strive for accumulation, for in the competitive environment in which he operates, one accumulates or one gets accumulated.
The stage is set and the characters take their places. But now the first difficulty appears. How, asks Marx, can profits exist in such a situation? If everything sells for its exact value, then who gets an unearned increment?”

Source: The Worldly Philosophers (1953), Chapter VI, Karl Marx, p. 148