During a recent writing session, I wrote a random piece about a cabin in the middle of nowhere, totally unfurnished, with no signs that it had ever been lived in or used. For something I pulled out of nowhere, it was alright. I don't consider it anything more than a writing exercise to get my mind started. However, I kept thinking about it.
Even though I created it, there was so much I didn't know about it, and I wanted to know what its deal was. Who made it? Why is it all alone? Was it abandoned? Were people abducted?
I realized that this little story was basically a piece of flash fiction, but it could be bigger. By writing about its history and explaining how it became the way it is, I could turn it into a short story. By detailing all of those events into a narrative, I could turn it into a novel. By zooming out into the world around the cabin and all of the other people who were affected similarly, I could create a series of novels. By thoroughly examining the entirety of the world in which those stories take place, I could create an encyclopedia.
No matter what, you can tell more. No matter how much of your world you do show, the universe is even bigger. You can show even more, or something different. The same process works in reverse. You could have a massive world and timeline that you create, but maybe the whole story that you want to share only is three sentences long. It's ok if that happens. You will always know more than your audience. That's just the nature of creating the universe.