I recently gave a reading from my novel-in-progress, and the section I read from was told from the perspective of a woman who, raised in a secular Jewish home in New York City and Westchester and having spent much of her teenage years in serious trouble (drugs, promscuity, bad grades, etc.), finds herself in Jerusalem in her early twenties and ends up becoming an Orthodox Jew. The section I read from, though it posited as its starting point the woman's religious transformation (she's now married to another newly religious Jew, and the mother of their four children) focuses in some detail on the character's travails when she was a teenager. Perhaps because the material I read from was fairly sexually explicit and I was reading at a synagogue, the reading inspired some discomfort among the attendees, particularly from one elderly woman who wanted to know why. Why were my characters the way they were? Why, specifically, was the young woman I was writing about so promiscous, and was the reason she later became an Orthodox Jew because she was tired of being promiscuous?
Though I'm not sure I managed to convince her, I tried to explain to this woman that fiction isn't about reasons--or, at least, that it's not about the kinds of reasons that can be reduced to a simple (or even not so simple) answer at a book reading. Fiction is about plausibility, certainly, but to make something plausible (to make your characters and their predicaments come to life, that is), is different from explaining them or giving a reason for who/what they are. Fiction is like love. It just is. As soon as you need to explain it, something has gone wrong.
Another way to put it is that fiction is about mystery, and the job of the fiction writer is to evoke that mystery, to embody it, but never to explain it. Why was my character so promiscuous? Why did she become an Orthodox Jew? Who knows? I don't mean that in a flip, offhand way. I'm the writer; if I don't know, who will? But there's knowing and there's knowing, and there's dramatization and there's explanation. A novelist dramatizes; he doesn't explain. Yes, he might provide some clues as to why someone acts as they act, but the reasons should never be simple, linear, or reductively causal. Who are we? How did we become who we are? These questions are essentially unknowable, and it isn't fiction's job to pretend otherwise. Because answers, as soon as they get articulated as such, inevitably obscure more than they illuminate.
My job as a fiction writer is not to reduce my characters' choices to an easy psychological explanation. My job is to render my characters in sufficiently convincing detail that they feel utterly true. My job is to make them come to life. I'm reminded of Martin Amis's novel THE INFORMATION, in which the protagonist, a novelist on book tour, is asked what his book is about, and he answers (I'm going on memory here): "My book isn't about anything. It is what it is. All two hundred thousand words of it. If I could have said it in fewer I would have."