This thesis aims to contribute to the discussion on the clinic of so-called borderline cases from an investigation into the intersubjective elements that constitute the beginnings of the psyche. The conductive thread consists of the paradoxical experience of dual unit, characteristic of the initial moments of relationability, and which also constitutes a starting point for analytical work with very regressed patients. To this end, this research will be divided into two thematic axes. The first axis, composed of the first two chapters, consists of an investigation into the beginnings of the psyche in sufficiently good conditions and then on environmental failures and their vicissitudes for the etiology of limit cases. The second axis refers to a discussion on the clinic of limit cases. Initially, an articulation of the main elements of early intersubjective experience with the concept of countertransference is considered. Then, the analytical work is proposed with the so-called difficult cases from a Transformational Model. This occurs within the scope of a field optician in which the non-symbolized psychic elements can be welcomed, metabolized and transformed within the analyst/analyzing dyade, considered as one of the pathways of this field.