Albero

But the putting of labour-power into action – i.e., the work – is the active expression of the labourer's own life. And this life activity he sells to another person in order to secure the necessary means of life. His life-activity, therefore, is but a means of securing his own existence. He works that he may keep alive. He does not count the labour itself as a part of his life; it is rather a sacrifice of his life. It is a commodity that he has auctioned off to another. The product of his activity, therefore, is not the aim of his activity. What he produces for himself is not the silk that he weaves, not the gold that he draws up the mining shaft, not the palace that he builds. What he produces for himself is wages; and the silk, the gold, and the palace are resolved for him into a certain quantity of necessaries of life, perhaps into a cotton jacket, into copper coins, and into a basement dwelling. And the labourer who for 12 hours long, weaves, spins, bores, turns, builds, shovels, breaks stone, carries hods, and so on – is this 12 hours' weaving, spinning, boring, turning, building, shovelling, stone-breaking, regarded by him as a manifestation of life, as life? Quite the contrary. Life for him begins where this activity ceases, at the table, at the tavern, in bed. The 12 hours' work, on the other hand, has no meaning for him as weaving, spinning, boring, and so on, but only as earnings, which enable him to sit down at a table, to take his seat in the tavern, and to lie down in a bed. If the silk-worm's object in spinning were to prolong its existence as caterpillar, it would be a perfect example of a wage-worker.
-Karl Marx

Lastly, the external character of labor for the worker appears in the fact that it is not his own, but someone else’s, that it does not belong to him, that in it he belongs, not to himself, but to another. Just as in religion the spontaneous activity of the human imagination, of the human brain and the human heart, operates on the individual independently of him – that is, operates as an alien, divine or diabolical activity – so is the worker’s activity not his spontaneous activity. It belongs to another; it is the loss of his self. Lastly, the external character of labor for the worker appears in the fact that it is not his own, but someone else’s, that it does not belong to him, that in it he belongs, not to himself, but to another. Just as in religion the spontaneous activity of the human imagination, of the human brain and the human heart, operates on the individual independently of him – that is, operates as an alien, divine or diabolical activity – so is the worker’s activity not his spontaneous activity. It belongs to another; it is the loss of his self.
-Marx