Introspection can be lethal for a writer. Then again, so can water if you drink too much. If you can moderate your intake, it sustains you.
A writer doesn't work with pen and paper. We draw from our reflections, often painful or erstwhile private. Unfortunately, once we stick our pens in this dark fountain, we get addicted.
Some writers are accused of being narcissistic bordering on solipsistic, as though no one exists outside of our writing - at least no one with more depth than the people we create. Rather, writers are almost pathologically introspective. The world outside might not scare us, but we move through it as perpetual outsiders, absorbing and regurgitating on the page to give us a way to belong. The whole business of fiction is being dissatisfied with reality and trying to gradually substitute our own or reflecting what we have witnessed through our funhouse mirror.
No other animal has mastered written communication. Our human brains understand that being a writer is an unnatural occupation, taking up time better spent on the hunt or with our tribe. There is a reason for the cliché of the author slouched over a typewriter in the dark, surrounded by cigarette butts and cold, half-empty cups of coffee, pasty from a lack of sun, weeks between significant human interactions. To craft worlds, we leave this one more than is healthy, especially given that the worlds we visit instead exist only in our pasts or minds.
(Writers, in my experience, do not have a tribe. Like any other territorial beast, we acknowledge one another with nods and grunts, but we mostly keep away from anyone and anything that is intent to interfere with our work. Other writers are competition for the finite resources of reader attention and are to be treated with suspicion.)
Writers cannot be happy full-time or we would not find the drive to write. Burdened with the infestation of thoughts we foster, happiness gets crowded out. We can get portions of it back and can even manage to create for minutes at a time with a smile on our faces, but we have lent our souls to greedy spirits. Writing is all about examining demons in seclusion. You know what Nietzsche said about getting into a staring contests with the abyss. It's often the only one we can get to notice our work.
We are perfectionists, of course, which only aggravates our condition because we do not live in a perfect world. Leonardo da Vinci supposedly said, "Art is never finished, only abandoned." Left to my own devices, in a world where I didn't have to try to be a success and had forever, I would procrastinate by rewriting until I turned gray. Nothing would ever be to my satisfaction because I learn so much by the end of the work that the beginning is now flaccid and in need of a rewrite. I release my work like a premature baby, hoping I have gestated it just long enough that it can survive in the open air. I don't think I could ever have it in me long enough to be confident it was ready, but I know I will burst messily if I don't get it out of me, naturally or via caesarian.
The great writers, the ones you remember from your freshman English seminar, were all limping from battles often left off the page. Your minor writers, the woman selling cheap paperbacks off a card table, can afford not to delve too deeply. You won't touch greatness at the bottom, but you won't drown. It is a decent trade-off, all things considered. We have small lungs and grasping hands. Most of us are not built for the swim.
The audience most cares about an artist once the introspection has conquered them. After years of calling their music caterwauling, many of my peers came in the day after Kurt Cobain's death wearing crisp Nirvana t-shirts. Elliott Smith's suicide via a knife to the heart (twice!) canonized him as a musical god, something that a life of suffering while he was called a sellout would never have done. If the story is never going to be finished to your satisfaction, at least leave the observer guessing at what might have been. It is glib to say their sacrifice was worth an early death. It encourages contagious suicide of those who would rather be appreciated than alive.
Like anything, the poison is in the dose. Some introspection deepens one and gives a perspective that might otherwise be lacking. Beyond a certain point, introspection is a tar pit from which we may never extract ourselves. It is a remarkably thin margin between the two and we often do not realize when we've gone too far into the muck to return to dry land.
But what is the alternative? Not visiting that source of our creativity? The Oracle of Delphi breathed toxic fumes, but she channeled messages from the gods. Surely we can withstand increasing tastes of introspection if it means we manage a slightly greater chance of creating something that will outlast us. We are not people, we are incubators. Our works take the light out of us to grow strong.
We don't stop because we cannot, because for all our doubt and communicable cynicism, we know we have a chance to write better than we have before and have the world care. We do it because it is our purpose and therapy, even when we only need the therapy because we are obsessed with the introspection that allows us to create. It is an artistic ouroboros.