When I occasionally attend conventions and/or talk with writers at them, I often give them what I call the Golden Rule of Writing Fiction: Stop thinking about yourself, and start thinking about your reader.
Writers are often introspective people who take their own experiences as a jumping-off point for a book. That is fine. But good fiction should not parallel the daily life of the novelist. Why not? In a word, this approach is boring 99% of the time. In the business, we often call a writer-not-very-cleverly-disguised-as-protagonist a "self-insertion." The only time I can really think of a self-insertion working to the benefit of a book is Stephen King's Misery.
Good mysteries are metafiction. They strip away the mundane routines of everyday life and turn it into something exciting, puzzling, and intriguing. They generally are not a psychotherapy session writ large. A journal is the place for a writer to work out his or her issues, not a mystery novel. Why? Because your readers don't want to hear about your problems. They have problems of their own, and whether they are consciously aware of this or not, they pick up a novel because it creates a barrier between the real world and a fictional world to which they can escape. They look for books by writers who can create an alternate world that's somewhat modeled on our own but obeys a set of rules found only in novels, where investigations are compressed into a one-week period, that sexy detective goes from nemesis to lover in the space of three days, and a protagonist manages to learn a very specific lesson and "evolve" by the end of the book.
If readers wanted to pick up the true story of a person hitting the skids and working out his or her issues, they'll read Augusten Burroughs or James Frey, or any other work marketed as a "true story." But of course the autobiographies of Frey and Burroughs--like so many, perhaps all, others--are fictionalized to a greater or lesser extent. This is why so many of us in the industry shook our heads in disgust at Oprah's rants regarding Frey's fictionalizing. Someday Oprah will publish her own autobiography, and I will be surprised beyond belief if it is not, in the immortal words of Bart Simpson, "self-serving, with many glaring omissions." Frey was smart enough to understand where his own storyline became dull, so he made up for it. That's what fiction allows you to do--to keep "life" interesting from the first page through the last. (And as for why publishers are shelling out big bucks for stories like Frey's--that is a whole 'nother issue....)
I always get a bit of a creepy feeling when I get one of those unprocessed, unconsidered autobiographical manuscripts. Within five pages I think, "OK, here's a story about a man whose wife has just died and who is feeling alone. The writer is a man whose wife has just died and who is feeling alone." Or "Here's the story of a detective who has struggled with depression and men. The writer is a woman who has struggled with depression and women." The problem with these stories is how unfiltered they are, how weighted down they feel right from the beginning.
Can personal experience be used to enrich a manuscript? Absolutely. But the best writers reconfigure that experience, transforming it into something more narratively rich and telescoping it into 70,000 words with a beginning, middle, and end. They look at their experience, re-envision it in fictional terms, reconceiving it to make it better fit the conventions, and think about the reader's experience of the printed book--and they do very much what James Frey did. This is why, when you meet the best-selling writers at conventions or at book signings, you see just a bit of their hero or heroine in them, but you still walk away thinking, "Interesting. Sue Grafton isn't Kinsey Millhone, after all. And Harlan Coben isn't Myron Bolitar. How did that happen?"