Full Idea
Dasein is an entity which does not just occur among other entities. Rather it is ontically distinguished by the fact that, in its very Being, that Being is an issue for it.
Gist of Idea
Dasein is a mode of Being distinguished by concern for its own Being
Source
Martin Heidegger (Being and Time [1927], Intro I.04)
Book Reference
Heidegger,Martin: 'Being and Time' [Blackwell 1962], p.32
A Reaction
How do you distinguish the Being of normal humans from the Being of someone in a deep coma, who has no existential issues? Has that Dasein ceased to be? Why does angst create a new mode of Being, but flying doesn't?