it is in so far as the third, the big Other, intervenes in this relationship of the ego to the small other, that something can function which involves the fecundity of the narcissistic relationship itself
Lacan argues that the Big Other’s intervention in the ego–small-other dyad is the structural condition that makes narcissistic identification productive rather than merely self-enclosed, exemplified by the child’s turn toward the adult during the mirror encounter.
, The Seminar of Jacques Lacan, Book VIII: Transference, 2015thesis