A person that can’t change their mind and won’t change the subject is a fanatic. You have met one before, they’re the people that won’t shut up about something you stop caring about or a subject you never cared about. Why is this person babbling on when you clearly don’t care? Simple: they don’t care about your time.
A fanatic has all of the time in the world for the subject that has taken control of their brain. They may no longer even be capable of talking about something interesting. It is possible that they have never had their own opinions and are now just a broken record of sales pitches or things they heard on the news.
A fanatic doesn’t need you to agree with them. The main objective of their incessant nagging/preaching/spewing of bullshit is to wear you down. They either want you to give in and buy something useless, give up and stop opposing their obnoxiously overstated opinion, or lose it and become a fanatic yourself. You absolutely should not choose any of these options.
There is little to no point of trying to engage in dialogue with this person. After a brief amount of discussion, you will quickly realize that they aren’t interested in facts. However, if you must talk to this person I’d recommend constantly interjecting with the dumbest questions you can think of. Stupidity will probably play strongly into their hands and you don’t have to pay attention to ask stupid questions.
Above all else DO NOT ARGUE WITH A FANATIC. As Mark Twain once said “never argue with a fool. Onlookers may not be able to tell the difference”. You cannot change the mind of a fanatic; there probably isn’t any mind left in there to change, and you may lose yours. Worse yet, you yourself could become fanatical.
Shy away from fanatics, definitely avoid becoming one. If your friends or family have become fanatics ignore them to the best of your abilities and hope their sanity returns. Do not allow yourself to be pulled into the stupidity. I think Mark Twain said it best “never argue with stupid people, they will drag you down to their level and then beat you with experience”. Don’t gain experience in fanatical stupidity.