All difference is apprehended by the perception of the tangible realities that constitute it, giving rise to ideational contents and feelings, and by a nontangible reality, lack, which gives rise neither to ideation nor sensation, but to traumatic experiences due to the connection between this perception and extinctive drive tendencies. The alternation absence-presence induces such an effect of difference, calling for psychic work which transforms the traumatic awakening into a sense of lack. The mind has two means available to deal with the traumatic dimension: it can put the traumatic experience into abeyance and employ hallucinatory modes of functioning. This allows it to make something absent without losing it and to make something present during its absence. By following the regressive path back to the drive source and by realizing the process of libidinal sympathetic excitation, this mental work results in a libidinal regeneration of cathexes. Libidogenesis is the après-coup of the work of lack.