In fact, the question is not as obvious in its answer as it might appear. I heard a talk by a professor of psychology many years back when I was working in that area. She told of a woman who was beset by voices in the head that “told her things”. Apparently, she had about three of these voices. The voices were distinct and had separate characters and didn’t always agree with each other.
The constant talk was causing her distress, depression and mental exhaustion because she felt compelled to join in these conversations in her head. This led to her constantly telling the voices that they were wrong, rather like an atheist belonging to some Christian forum and 24/7 being given a constant stream of repetitive pseudo-arguments to refute.
The professor explained that although the symptoms were not severe and the woman still had a grip on life, battling these voices was, for the patient, the most troubling aspect of psychiatric illness.
The professor then realised that throughout human history, people with bizarre thought processes had, nevertheless, become happy and, in some cases, great, as there was a level at which the ‘normal’ person would accept the logic. Think of New Age beliefs, crystals, aromatherapy, chiropractors, homeopathy, etc. and also those in the Bible who claimed “God spoke to me and said…”.
What the professor now did was to give the woman a course in cognitive behavioural therapy and a course in management. The latter focussed upon effective chairmanship of meetings.
The woman was receptive and, soon, instead of arguing with the voices, she took control of them by saying such things as, “I don’t think that suggestion is very helpful, do you? Could I ask you to concentrate on the matter in hand?” and other passive-aggressive tactics. Instead of having warring tribes in her head, the woman now had “cooperative friends” who were able to help her reason out problems and choices that she had.
As people in general are a bit worried by others who say they hear voices, the patient was also taught not to refer to “the voices” but, when explaining “their” arguments, to say things like, “The other day, a friend was saying to me …” or claim that it was her idea but (inside her head) credit the voices.
The professor concluded by saying that she had seen the woman recently and she was happy. She still had the voices which were not her friends and she had found that the woman’s circle of real friends had increased as people were coming to her for advice on social matters. There was a little more to it; the professor was not disappointed that the woman hadn’t entirely kept to the script and was claiming that the voices were “spirits” because séances are culturally acceptable.
I must emphasise that this will not be a solution in all, or perhaps even, in many cases. However, it does give some insight into borderline psychiatric disorders and is parallel to the solution applied in physical disorders -> if the patient cannot be cured, teach the patient to live with the illness/disability.