For years I thought of myself as strictly a short story man. I'd have a great new idea for a novel, and I'd be so excited to start writing, and… I'd wrap after ten or twenty pages.
Because the ideas were for a story outline, or a setting, or a cool concept – but not about characters or growth or conflict. I'd write basic boring characters just to fill the needs to explore these ideas I'd had.
Unsurprisingly (in hindsight), the first idea I had that was enough to carry a 100,000 word novel was one that was intimately tied to an actual character. The idea informed the character, and the character fleshed out the idea, and the world framework necessary to support that idea and character led to more ideas and characters, and I'd finally finished my first real novel!
From there it was much easier to write a second novel, because the same type of idea I'd always had before was now supported by a big cast of characters and an interesting setting.
So after talking about myself, I guess my advice is not to tell you your idea isn't a novel, but to really work on the implications of that idea. Think of how that idea affects people and the world, and hopefully you'll come up with some really cool characters and stories based on your original idea!
Source: reddit post