Growing an Idea

Sometimes the books I write go through their own journeys. My baseball novel started out as a story about a camping trip. It was based on a trip I took when I was eight. Here's a picture diagram I made for my students about how the story changed:

The original idea, first written as a boy mc and then changed to a girl, was a quiet story that my parents and sister still enjoy. After all, they lived it. As I nurtured this idea and watched it grow, rewrites and critique changed it into something completely different. The story the seed became is about a character who only exists in the world I created for her. But her world is as interesting, exciting, and full of drama as I could write it. Hers is a story to share. 

Have you ever started out with one idea and ended up with something completely different?