It's true when they say writing is like a muscle, needing exercise to grow. Since I've started writing a novel, just by writing, ideas for other stories, novels, and screenplays just keep coming.
Right now, I have a novel I'm writing, which still has a lot of work ahead before its a compelling finished product. But I have two others I could write, and an idea for a screenplay. This being my hobby, this is easily years of writing, all lined up in the tank (i.e. in notebooks and in my head). A year ago, I had no ideas for a novel. I labored under the notion that other writers had great ideas, and I had nothing to write about. And that even if I did, I was terrified of actually starting. Scared that I might begin and only realize it's all just awful and I'm pecking away at a masterful craft with absolutely no tools behind me.
There are still many times when I fear my vocabulary is inferior, and my descriptions lacking, especially when I read exceptional novels. But I don't let it get me down (most days) and keep plugging, working towards my weekly goals. Some weeks I meet them, others I fail. I climb small hills, knowing that they are part of a mountain, really, and when I turn around and look back down at the ground I've covered, it's breathtaking. I look up and see how far there is still to go. It's good. I am a pretty good writer, in that I'm well-practiced, and I enjoy it. I have an decent vocabulary and I find that the characters I write don't always need to use a fancy word, nor would they know it to use it anyway. I build my skills by writing more, and by reading. I am a student of the craft. But not the one who learns in theory. It comes from practice, more practice, and then more.
I am so thankful to have this initial story to inspire me, to get me to begin writing fiction. Using a real-life inspiration. But that was all it took. It was exactly like this proverbial floodgate, that once I found myself thinking on an almost-daily basis about the lives, decisions, and barriers in my characters' lives, it becomes easier to imagine the what-ifs of a thousand other characters too.
What if a woman on her way to a job interview has to take a detour because of construction, and then her car breaks down, so she gets out on foot; but on the way to the interview (she's now sweaty and quite late), a group of fantastical dwarfs intercept her and recruit her to help them save a princess captured by their enemies? [Based on an actual dream I had. Thanks, brain.]
These are the kinds of scenarios that begin novels, and before my writing muscles weren't strong enough to challenge my brain to see them, all the multitude of what-ifs out there, everyday, that inspire entire universes and spawn the characters we come to admire or loathe and everything in between.
They're already there. I just wasn't exercising enough. I've also learned that you don't have to know the whole story before you sit down. You just have to start with a character, with a desire, and a challenge. I'd heard it before, but that is different, entirely, from sitting down in my chair and writing it. And learning it, understanding what all those other writers says when their best advice is just to sit down, every day or almost every day, and let it come out.