I know that this question may be for a more psychology-focus forum, and "great" is an understatement for players such as Fischer; yet, I want to know your opinion on this question. Is it intelligence? Is it pressure? Or is it the game itself? Whatever is the ultimate answer, I wonder if the grand gift or talent has a big backlash, or even at a lower level of play, does playing game become harmful then?
King's Gambit: A Son, A Father, and the World's Most Dangerous Game is about this. The age-old question is:
Does chess make you mentally ill or are mentally ill people attracted to chess?
There's a whole bunch of other supporting facts about chess being linked to insanity, but I'd have to re-read the book to recall all of them.
All the insanely brilliant people in my life have some form of mental illness. I consider myself extremely fortunate to know these people. They're genius about things I can't begin to understand. There's two bipolar geniuses and two Aspergers geniuses. I know three of the four love chess.
And then there's my 135 IQ friend who's bipolar, her boyfriend from back in the day who was a genius and schizophrenic, my straight A friend who's depressed and maybe a little autistic, my aspergers 130+ IQ friend, my nerdy (aka autistic/aspergers traits) friend with depression who's 138.
So basically every intelligent person I can name has some sort of "disorder." Remember that by definition, being intelligent isn't normal. Who's to say one is the correct or incorrect way to think? Just because the majority of people think at a normal intelligence doesn't necessarily mean that's the right way to think. That's just how almost everyone thinks, so they only diagnose the exceptional people. Maybe you could argue that having a normal level of intelligence should be its own mental disorder.
For example, normal people don't get intelligent questions. Look at some questions on here written by geniuses and you'll see they're immediately flagged and closed. People rationalize it after the fact. It's unfocused, or too specific, or not a real question, or misguided, or all over the place, or off topic, or whatever. The kind of thinking that seems obvious to the intelligent person needs to be justified to normal people. Remember that as a society we villainize intelligence. Nobody normal is interested in big ideas. That's weird. All they care about is whether or not this is going to make their life more comfortable. And I'm not really sure why we were put on this Earth, but I'm pretty darn sure it wasn't to make ourselves comfortable.
See where I'm going with this?
My Calc professor left his copy of that book on my desk the day I went in to take my final exam for his class. He loves chess and mathematics. I'd visit him in his office after my class ended to say hi. We'd talk about intellectual giants and infinity and chess. Sometimes you can get caught on a problem, and start thinking about it forever. And eventually it'll drive you crazy. That's what happened to a lot of these mathematicians. Maybe these chess guys just got too absorbed in their own world. But it takes a tremendous mind to be capable of creating a world.
See where I'm going with this?
I think great talent and great psychological instability can go very well along in an altogether very unbalanced life.
I don't think the game in itself causes that, nor that being crazy¹ helps² to play, only that concentrating the focus of a lifetime to a single thing can very wall harm one's sanity.
Cantor comes to mind, relatedly.
¹ In all it's fuzziness. Define “crazy” if you want answers to try and be objective.