Aside form those reasons, I believe the most common explanation for an individual being under the misapprehension they have magical power, is they don't have any close friends. Let me explain.
When I was sixteen I was convinced that wearing cowboy boots with lederhosen would not only get me girls, it would start a new fashion trend which would rival the great fur underwear movement of the nineteen-tens. Luckily, I had several close friends who beat me mercilessly every time I left home in my German mini-pants. Because of this I quickly learned that dressing like a drunken Oktoberfest cowboy was not only a poor fashion choice, it got me kicked in the balls a lot.
This hard learned lesson didn't just teach me the folly of acting out my every whacky thought, but also the importance of honesty when it comes to telling your friends how stupid they are, even if they don't want to hear it, like Finnegan.
Before Finnegan's smelly demise he and I had many conversations about his "abilities," which tended to end the same way every time; with him trying to read my mind or predict my future, and me getting drunk and calling him an ass-hole. And just so you don't think I'm a jerk, he really was an ass-hole.
I proved to him again and again that his so called powers were no more real than my enthusiasm for an all female Ghostbusters remake, but no amount of logic or reason would penetrate that puss filled melon he called a head.
Once he had me shuffle a pack of cards then flip them over one at a time while he attempted to predict each card before it's revelation. Of the fifty-two cards in the deck, Finnegan managed one correct guess. When I pointed out how pitiful this score was he complained of alien interference and locked himself in the bathroom until I went home.
Another time I was lamenting how I had placed five brand new hundred dollar bills in one of my books but could no longer remember which of my many books it was. Without hesitating, Finnegan rolled his eyes back in his head and started chanting to himself with the energy of a Trump protester hopped up on Red Bull. When his eyes snapped back into place he loudly declared, "Your money is on page 237 of, How to Castrate a Penguin." When I told him he was wrong because that book only contained eleven pages, he called me a liar and knocked the jar of pickled crackers (also known as 'mush') out of my hand. When I showed him the book several days later he still refused to accept or acknowledge his mistake.
I've noticed this refusal to admit glairing errors even after being proven wrong to be common among those dwelling in the world of spirituality. Cognitive dissonance drips from their superstitious pores like slobber from Jabba The Hut, and no amount of evidence, logic, or smacks in the face with a wet sock, will get them to acknowledge their blunder.
Perhaps if I had been a better friend to Finnegan I could have convinced him his delusions of clairvoyance were nothing more than the misfiring of rotten neurons in his useless mind, but alas, I found it much more entertaining to call him names and hit on his wife when he left the room.
I guess what I'm trying to say is, I'm glad he's dead and the world is a much better place for it. Not because he was a bad guy who cheated on his taxes or shit in the street, but because his type of mindset was not one conducive to the advancement of a modern, scientific, society. In fact, his interpretation of the world was the same one that had "doctors" drilling holes into the heads of epileptics to release the spirits that dwelled within, and priests mumbling over gangrenous limbs in the hopes God would lick the wound clean.
So, goodbye Finnegan, I'll miss you and all the good times we had and just in case you happen to have been correct about the dead being able to observe the living, sorry about sleeping with your wife after the funeral.