I think it depends on why you're in therapy in the first place. What are you trying to fix? What are you trying to change?

When that is fixed/changed, then maybe you're done.

Or maybe you uncover other things during the process that you want to fix, or improve. So then you work on that. So it could be an endless process. Or maybe you get to the point where you think that you're "good enough" and you can handle anything else yourself.