Everyone has moments in life where things could have gone one way or the other. I'll always wonder what would have happened if I chosen to go to IU for college, instead of Butler, or if I hadn't moved to Los Angeles for two years for grad school.
Or if I had stayed with my original life plan and became a music teacher.
Write the story of your own life if you change one of the big decisions.
This could also, of course, be a romantic choice. If you've ever been the point in a love triangle, imagine your life with the other person. Or, perhaps, imagine your life if you hadn't made the biggest error of your life by ruining your relationship with your love at the time, who dumped your ass cause you're a cheater. In the end, make sure the choice changed if yours - not someone else's.
And, of course, change all the names and call it fiction.