You've probably heard that characters have to change over the course of a book. Usually, characters will reach a turning point in which they learn a lesson, or conquer a fear, or accept the inevitable, or break out of a pattern, etc. The challenge is to write such moments without leading readers to roll their eyes and say, "It never happens that way in real life!"
And yes, few of us have apocalyptic battles with villains over the fate of the world. But people do have life-changing moments in which they decide where to go to college, whether to marry, or when to leave an abusive person behind. They decide to have babies, or stop drinking, or compete in the Iditarod, or join the Peace Corps, or enlist in the Army. Some of these changes are about taking the next steps in life, and some of them are about facing inner demons.
The question is, how do those moments come about? Sometimes they're the result of a sudden shock: the death of someone close to us, for example. Sometimes they creep up on us gradually, as when an unpleasant job or relationship becomes unbearable. Sometimes a person changes in order to get something he wants.
I can tell you the moment when I decided to apply to graduate school. I was talking to a friend about how I was "thinking" of doing it "someday," and she said, "You talk about this a lot. It sounds like you really want to do it." And I realized that yes, I did talk about it a lot, and it was time to stop talking and do something about it. My friend's remark was the trigger, but it was built on research and interest that had built over time.
Much fictional change is like that: a desire whispers in the main character's ear, and grows through the course of the novel. The reader sees it building, like a pile of kindling. At the peak of the story, someone lights a match, and the change is both sudden and an inevitable culmination of everything that came before. In a book, the inciting event will usually be a little more exciting than a friend's comment. But sometimes, the drama is not so much in the event as in what happens to the character as a result.