There's a great line from William Goldman's novel The Color of Light: "Life is material; you just have to live long enough to figure out how to use it."
William Faulkner maintained that any child who managed to live past the age of seven had enough material to write books and stories for the rest of his or her life and never see the well run dry; Flannery O'Connor said much the same thing.
All of which is a roundabout way of saying that if you encounter any author who insists that his/her work isn't in some form autobiographical, they're lying through their teeth.
It's not only outward, chronological events that shape our psyches and determine who we become, but our own internal worlds; imagination, impressions, prejudices, fantasies, regrets, passions, likes and dislikes, all of it is eventually filtered through the writer's sensibilities to make an appearance in their work.
Sometimes a writer has to wait until he or she has gotten enough distance, both emotionally and chronologically, to turn a fiction writer's objective eye on an event. You can't use an actual occurrence from your own life and then defend it to people by saying, "But that's how it really happened." Fiction cares nothing for how an event 'really' happened, only how said event or events fit into the natural progression of the story you're telling.
You have to learn to put your ego aside when you write a story or novel, even if you're using something from your life as fictional fodder; you have to care enough to be quiet. Let the story be your guide, not your desire to inflict yourself and your views on the reader.