Insomnia started out as an 800 word brain vomit flash piece written in response to a prompt. At the end the MC rescues the girl from death-by-truck, then walks off into the sunset. I liked it, but it needed more.
After a few revisions, turning more of the tell-ish scenes into show-ing scenes, I had the story Daily Science Fiction published. It was short, but not too short. It had a conflicted MC. It raised a lot of questions every time I read it. I didn't just like it, I loved it.
What had first piqued my interest in the idea was the concept that every choice we make influences the future. Not just our own future, but that of the entire world. Whether we stop to brush our teeth, whether we turn left instead of right, cross against traffic, or circle around the parking lot an extra time to try and find a spot closer to the store entrance. If these things really make a difference what sort of difference might be made by making all the "right" little choices.
Then I had my MC, a man who is part of a larger organization - technicians working with the data stream from the future, agents working in the field - dedicated to making sure the right decisions are made. An organization that is making some very wrong decisions when it comes individuals. (What is one life worth?)
And from that MC, a man who does bad things because he is told it will make the world better and safer, grew the ending of my story. It is not meant to be a "conclusion". If anything it is a question - can one man save or destroy the world by what he does? Even when it is the "right" thing?
I could have answered that question one way or another, but I chose not to. (Partly because I wasn't sure what the answer should be and partly because I'm perverse that way.)