Every person and every therapeutic pairing is unique. There is no rule about how long any therapy should take. Each person comes to therapy with her or his own combination of resources and problems, issues with trust, and means of processing new experiences. All of this affects the length of the therapy — whether it lasts 3 months, 3 years, or 3 decades. However, it is important that both therapist and client keep asking themselves (and sometimes, each other) whether the therapy is effective. If it doesn’t seem to be, they should talk about what isn’t working. If they can’t resolve whatever is causing the therapy to be stuck, they might consider transferring the client to a new therapist.
Remember: Change doesn't have to take years.