I have learned with autistic kids, that the best starting point is to meet them where they are, and work from there.
I recall in "A Beautiful Mind" John Nash COULD NOT accept that the delusions weren't real; logically he could understand (eventually) but it didn't stop them. I remember the scene where he bent down to talk to the little girl (who wasn't really there) and say to her, "I can't see you any more, baby girl." Although he knew the hallucination was not real, he still had to talk to her to say goodbye. He couldn't just switch off and walk away without looking back. It was an interesting point. And the delusions didn't stop.
I also saw in that film - it didn't matter how much he was told that things were not real - he had to see it for himself, he had to get to a point of realisation for himself.
Sometimes you need to say to someone, "I accept that this is your reality." That doesn't necessarily mean you are entering their delusion. But if constantly telling someone, "Honey, this isn't real" is not working, then maybe it's time to try something different?
Some time ago I was closely involved with some children who were in hospital for Chronic Fatigue Syndrome. The parents were restricted in when they could visit. The kids were actually being treated by a psychiatrist who was also a pediatrician. The parents were only told the "pediatrician" part. The kids were 'encouraged' by a reward/punishment system, to get up and about. Get active. A kid who felt too exhausted to get out of bed was penalised by not being permitted a letter from her parents. This treatment forced the kids to push themselves. Maybe some of those kids COULD do it if they pushed themselves, but others could not.
With time, the children learned that when asked how they felt, if they told the truth they would be punished. But if they lied and said, "I feel fine," that increased their chances of being allowed to go home.
The doctors thought they had cured the kids. Instead, they just taught them to hide their illness and to lie about it. Lying to their parents as well, because a kid's mother might go to the doctor to say, "You've bullied my kid into lying that she's well when she is not, you've denied her access to the TV I've been paying for, you won't let her friends visit - how do you think this is helping her?" This would result in the child being punished later on by the doctor, and also would teach the child to not tell the parents.
If we keep insisting to a delusional person that they are delusional, then we risk those delusions seeming more real than what we say. If I look at my table and see a cup of coffee there, if I can smell it, can pick it up and drink some - and you come and tell me it's not really there, who am I going to believe? You, or my own senses? And am I more likely, or less likely, to believe anything else you say?
But if instead you say to me, "I can't see the coffee cup, but I accept that you can see one," then the situation has changed. I feel less urgency to hang on to the delusion - it's not longer a "tis", "t'isn't" exchange.
I would be much more nervous if the therapist is saying that you have to drink an imaginary coffee too. I don't see how that can be in any way moving towards a return to reality.
But bear in mind - I am not an expert.
Marg