> the object which labor produces – labor's product – confronts it as something alien, as a power independent of the producer. The product of labor is labor which has been embodied in an object, which has become material: it is the objectification of labor. Labor’s realization is its objectification. Under these economic conditions this realization of labor appears as loss of realization for the workers; objectification as loss of the object and bondage to it; appropriation as estrangement, as alienation.
> [...]
> the worker is related to the product of labor as to an alien object. For on this premise it is clear that the more the worker spends himself, the more powerful becomes the alien world of objects which he creates over and against himself, the poorer he himself – his inner world – becomes, the less belongs to him as his own.
https://www.marxists.org/archive/marx/works/1844/manuscripts...