Full Idea
We are Dasein - the entity who possesses - as constitutive for its understanding of existence - an understanding of the Being of all entities of a character other than its own.
Clarification
'Dasein' roughly means 'existence' or 'being there'
Gist of Idea
For us, Being is constituted by awareness of other sorts of Being
Source
Martin Heidegger (Being and Time [1927], 34/13), quoted by Richard Polt - Heidegger: an introduction 3.§4
Book Reference
Polt,Richard: 'Heidegger: an introduction' [Routledge 2003], p.35
A Reaction
This seems to connect to the emerging 'externalist' view of mind that comes with the external view of content coming from Purnam's Twin Earth idea.