How, then, do Lacan’s ideas differ from the mainstream psychoanalytical schools of thought and from Freud himself?

With regard to other schools, the first thing that strikes the eye is the philosophical tenor of Lacan’s theory. For Lacan, psychoanalysis at its most fundamental is not a theory and technique of treating psychic disturbances, but a theory and practice which confronts individuals with the most radical dimension of human existence. It does not show an individual the way to accommodate him- or herself to the demands of social reality; it explains how something like “reality” constitutes itself in the first place. It does not merely enable a human being to accept the repressed truth about him – or herself; it explains how the dimension of truth emerges in human reality. In Lacan’s view, pathological formations like neuroses, psychoses and perversions, have the dignity of fundamental philosophical attitudes towards reality. When I suffer obsessional neurosis, this ‘illness’ colours my entire relationship to reality and defines the global structure of my personality. Lacan’s main critique of other psychoanalytic orientations concerns their clinical orientation: for Lacan, the goal of psychoanalytic treatment is not the patient’s well-being or successful social life or personal self-fulfilment, but to bring the patient to confront the elementary coordinates and deadlocks of his or her desire.

Slavoj Zizek, How to Read Lacan