My first thought is to say "this is the ideal case". It requires a strong client. Sometimes that is not the case -- a client who can (at least in the beginning) deal with big difficulties. Then it depends more on the skill, or correct techniques, the insight of the therapist. Sometimes they don't match what the client needs, good intentions to the contrary notwithstanding. If the T's abilities are not sufficient, the client may think it is her fault that the therapy is not working. And a destructive spiral may take place.

FWIW.