That makes a lot more sense to do the one-day-challenge for fun. It sounds like something entertaining, and that I may even try in the future (looking at a rather small-scale game, of course).
Regarding your comment on ass-pulling in order to reach an achieved ending, that's why it's good to work out an idea of the middle section of the story that leads from the beginning to the end. That way you have an idea of how that ending will be achieved. Of course, since we're talking about story games, it gets a little more complicated than that, but it's still possible to map things out vaguely and accommodate for multiple endings.
Loving the conversation thus far, everyone! Has really got me wanting to write!
I think I'm going to start writing one of my many story ideas now. I already have the basic pre-writing done, and I think I'll start trying to write without mapping out any of the specific branches/pages beforehand. What I have written is a general overview of the story, a beginning/middle/end(s) structure, main themes, and then random notes on the back story. We'll see how this goes with that much pre-writing!
Writing a story is a lot like driving a car. You need to have a very clear idea of where you want to go and what you'd like for your passenger (reader) to see. What places will you take them? What characters will you introduce them to? I think for starters, thinking up of a good plot is a good way to start any story. You need to know where your story is taking place before you can figure out how you want it to progress.