Dasein is an entity which is in each case I myself; its Being is in each case mine.Heidegger calls this just a (formal?) indication, and then tries to seperate this Being, the "I", that is Dasein, from the Cartesian subject, gazing out into a world of objects, as is the case with metaphysics. To wit:
It could be that the "who" of everyday Dasein just is not the "I myself".As Jean Grodin indicates:
P. 150
[W]ithout this opening, this fulguration of Being would not take place. However, man does not control this fulguration. He is there (hence the term Da-sein), he belongs to it, for he himself is a sudden emergence, a rest-less unfolding in the opening of the present. This is Heidegger's fundamental experience.That fulguration of being, of course, being enowning.
P. 26