Edward S. Casey and J. Melvin Woody on the basis for Lacan's subject who is "supposed to know".
But what is this subject, after all, this being who is defined by language and who becomes Other to himself by being in language? "What constitutes
me as subject is my question," remarks Lacan, echoing Heidegger's description of Dasein as a questioning being in the introduction to Being and Time. Questioning—whether of oneself, of other beings, or of Being itself—is itself a fundamental form of splitting within the subject, since it inexorably introduces a division between the questioner and the questioned, the known and the unknown. Lacan therefore speaks of the subject as "ex-centric," as alienated from himself. The philosophical origins of this conception of the subject again derive from Heidegger's analysis of subjectivity in Being and Time. In this work of 1927, Heidegger designates human existence as "Dasein": literally, being-there. To be-there is to ex-ist, to standout in one's being-in-the-world. Such ex-isting is a way in which to-be:
The 'essence' of this entity [Dasein] lies in its 'to be' [Zu-sein: about to be, implying possibility] The essence of Dasein lies in its existence. . . . In each case Dasein is its possibility. [P. 67-8]Dasein exists, then, by standing out—out from the world regarded as a collection of indifferent, present-at-hand particulars and out from itself as a centered substrate. As thus ex-centric and ex-static, Dasein stands out as being something other than its mundaneity or egocentricity would prescribe or predict; and it does so in two basic ways: (1) Dasein ex-ists by the projection of existentially significant possibilities through its understanding of the world and itself: an understanding that is essentially projective by virtue of its fore-structure, through which it is ineluctably drawn into the hermeneutical circle of knowing projectively what it comes to know in detail in cognitive (and other forms) of inquiry; and (2) Dasein also stands out from itself by its involvement with others in the "with-world" of human sociality, especially in the crucial activity of "leaping ahead" in relation to others rather than "leaping in" for them by directly disburdening them of their anxiety or cares—where "leaping ahead" has remarkable affinities with psychoanalytic techniques of abstinence, silence, and empathic understanding. Such leaping ahead contrasts with the deadened and deadening passivity of das Man understood as the "they-self" which dictates conformity and submission.
Pp. 203-4, Volume II