Every writer has thought of a good idea, explored in his imagination how the story might develop and the characters will work. Every writer has let himself become distracted for a bit and then forgotten it all.
I haven’t written much lately, but while I was working on computer program here at work, I thought of a nice idea for a story. I saved my work, found the icon for my word processor and then started that up. My fingers were set to type, but in that short time I had completely forgotten the idea. All I had was hole in my memory where the story had lived temporarily.
This is frustrating. I keep a pen near my bed in case I think of something in the night. I keep a pen and notebook in my computer bag so I can write down things that I think of. I keep notes programs on my phone and iPad so I can record ideas. This, however, happened at my desk at work. I like to knock off 15 minutes before I leave and fiddle with a story idea. This is where I write, so it is frustrating to forget a story so easily.
The problem was that I had not completely solved the programming problem that I was working on. My mind was still trying to work out the IFs, LOOPS, INPUTs and OUTPUTs of my program, so that I stopped thinking about the story while I saved my work and opened the word processor. In that moment of inattention, the line of thought was lost.