I get one idea, one tiny little thing, then build off of it. Like I have an idea for a creature in my book, boom, now I have a magic system that works with the creature. Then I tweak it over 3.5 years until I’m happy with the maid system, and I’ll continue to tweak it. Often, in the process, the original idea is fossilized, where it is similar to the original but made of something completely different.