Describe "decompensation" to me

Apparently this is what happens when a narcs grandiosity isn't validated by reality. When you think about it, this is probably going to happen eventually with certain people; they think they are the greatest person who ever lived, but this notion is constantly invalidated by others, and eventually they cannot hold this fact about themselves anymore, and then they start to decompensate into a paranoid disorder or complete ego dissolution. I mean it's basically impossible for every person out there to confirm this.

So what would said person do to avoid this? Would they just force themselves to believe they are on "the same level" as everyone else, just a regular person who isn't any more grandiose than the average joe, and then they wouldn't decompensate.

Would they brush off the invalidating comments by others, but get their supply elsewhere? The problem with this though is that the amount of validation they get to believe they are "the king", so to speak, would likely be far less than the amount of invalidation they get from most people. So wouldn't they decompensate then?

What would this person do? Perhaps you've experienced this before yourself.

Loooong agoooo there was a boy called J. He had a mother, called Madame S. She was so fat that she barely fit through the door and was convinced that she was the center of the universe. J was her youngest son and under the guise of protection[ism] she would enter the room without knocking, plug into his phone calls, talk for him in conversations, conversations that were mostly about herself in some or the other way then, she or her husband would also come into the room and get files from a cabinet that was apparently only in the room so they would have a reason to randomly come in. Above all she was French so she still always demanded l'embrasse of teh poor guy who was 17 or 18 back then lol. In any event it was a classical living-thru-projection-of-kid parent-child thing, where she and her hsband also had clear ideas of what was acceptible and what not, what he should later do and what not, what grades he has to have, which people he should associate with. Nevertheless, eventhough she was controlling, and ridiculously unaware of the existence of other people, there was a semblance of contentedness.
Many years later Akuma was at the doctors place for some reason when he heard the assistants apparently trying to control someone, saying "Madame S. please dont disturb the other patients. Madame S. you will soon be called in. Madame S. please stop that." Akuma chuckled and finally that mysterious Madame with the last name he associated as much pain as happiness with came into the waiting room. The face still the same sure, but she had lost about 40cm of her waist it seemed and she was extrmely distraught. She walked back and forth, sat down, stood up, listened to some music, looked into her purse, into her jacket, into her bag, it was almost liek some buggy endless loop of a search algorithm. Finally she stood up, approached Akuma and put her ear-plug-headphones to his ear saying "Listen, isnt this music great!?", seemingly without conscious awareness of that he had once been a regular guest in their household. Akuma smiled at her and told her that his stepfather would love that music [it was horrible german volksmusik] and noticed one of the assistants in the door looking desperate but relaxing a bit when Madame S. walked back to her chair again. Akuma was then called into the doctors office before he could decide if he should speak to Madame S. and when he came out she was gone.