Remember 細い and how it means "thin." Well, this is another adjective that comes from the kanji 細 with a similar but different meaning (sorry!). If you think about something that's very thin, though, there isn't much surface area. In order to use this very thin thing (say, to put your favorite model railroad on) you have to zoom way in and get incredibly detailed with it. It's super small and fine, so get your magnifying lens out! You can remember that this one is "detailed" or "fine" because the かい makes you think of coyotes. You put a ton of work into this detailed and fine model railroad on a very thin piece of land. Then, a coyote comes in and trashes it all, because you made the mistake of making it out of meat.