Just what is the story trigger? When I'm planning a story in my head, I hear "Wait for it, wait for it." Suddenly a change in one of the character's lives appears and I know this is where the story will begin. With a change.
No matter what kind of story you're writing there is an instant of change. Right now I'm writing a cozy mystery. As I pondered how to start the story. Then my heroine of the series sees a For Rent sign on the house next door. I knew then the new owner would bring the change into the heroine's life. In a romance of mine, the hero arrives in town and goes looking for the heroine, the woman he once loved. He goes looking for her. She is a doctor and he is a nurse, a new hire at the hospital. He arrives for a medical examination. And there both his life and that of the heroine change. Some day I'll write a fantasy that will begin with this line. "The emperor is dead and his daughter is missing." Once again a change.
All through each story, there will be points of change driving the story forward. The good thing is that every change keeps the reader turning pages. But just a change isn't enough. The change must drive the character toward or away form his or her goal. This change must be inside the character and also in the outer story.
So embrace change when you're telling a story. Change will trigger the story forward.