In all the abovementioned meanings or contexts the uncanny is,
according to Heidegger, the opposite of homely, familiar, understood, and
assimilated. In Being and Time – where Unheimlichkeit functions as a tool which allows structural description of existence, as Dasein’s being-in-the-world (understood above all in terms of ‘dwelling with...’, ‘being familiar with...’, care) – Heidegger defines the uncanny as unsettlement, rootlessness, nothing and nowhere, being ‘not-at-home’. Unheimlichkeit is, therefore, a specific attunement of Dasein, encountered in anxiety which is a kind of a fear that does not have a particular point of reference, and which shatters the very fundaments of existence. “Everyday familiarity collapses” – states Heidegger: “Being-in enters the existence of not-being-at-home. To talk about ‘uncanniness' means nothing other than this.”
Thus, the uncanny is being-in-the-world as un-familiarity, which means that this world – so far familiar and domesticated – starts to appear incomprehensible, foreign. Experienced in anxiety, uncanniness suddenly exposes to Dasein the fact that that the organized and meaningful world which used to be Dasein’s home is not a home anymore. “(...) Our heedful awaiting finds nothing in terms of which it could understand itself, it grasps at the nothingness of the world” – describes Heidegger. Therefore, all that is experienced by Dasein – every thing and every thought – presents itself as empty or meaningless, since it does not have any meaning for or any relation to Dasein’s existence. Hence, in uncanniness one cannot find anything that would help one to understand oneself and the surrounding word. All conventionalized and common (shared) meanings – Heideggerian the ‘they’ which enable to organize the reality of everyday experience – become invalid. From the perspective of the experience of uncanniness, every action and effort to communicate seems to be doomed to failure. The world is thus radically unfamiliar.