The word "insane" is one we tend to toss around easily without much thought most of the time (never mind the word "crazy"), but the details of mental illness and imbalance are at once horrible and fascinating.
I never really considered it as a resource for writing until I was initially trying to get to know the characters in my first Varin novel, and decided that in order for it to be as realistic as I wanted, the "evil king" character had to be inbred and mentally imbalanced. That sent me off into a whole bunch of encyclopedia research on mental illness until I found pathologies that matched his behavior (in this case, obsessive-compulsive disorder and paranoia). For a time, my husband worked at a company that offered continuing education courses to medical professionals, and several of the seminar topics related to mental illness, so I gathered quite a bit there as well.
Then I read The Midnight Disease: the drive to write, writer's block, and the creative brain, by Alice Flaherty.
That book is a revelation, and I encourage all of you out there to pick it up. It's not a difficult read at all, and it's amazing. The author talks about her own experiences with hypergraphia - the uncontrollable urge to write - and about all kinds of famous writers and creative minds which also happened to be not quite balanced.
One of the most fascinating things that Flaherty discusses is the possibility of an evolutionary link between creativity and insanity. Insanity is not exactly what you'd call an adaptively successful trait - but if it's the unfortunate product of overconcentration of the genes that give us creativity, then you can easily see how the success of highly creative individuals in natural selection would mean that the possibility of insanity would never quite go away.
I compare it to the case of sickle-cell anemia. A person with two matching genes for sickle-cell anemia gets the disease and is very ill. But a person with only one of these genes has a higher resistance to malaria than a person who doesn't have the gene at all. So the adaptive success of the single-gene trait leads to the continued presence of the disease itself.
Since reading that book, I have in fact written a character who suffers from hypergraphia. Let's just say it was a serious inspiration.
At this point I'm going to have to close this post - but I think I'll come back to the topic because there are a couple of things I'd love to talk about that relate to it tangentially, specifically:
1. unreliable narrators
2. narrative voice
Hopefully I'll get to writing those in the next couple of days. If in the meantime you have anything you'd like to contribute to my preparation for such a discussion (questions, comments, etc.) please feeel free to comment.