I think sometimes readers, and writers alike, forget that stories don't always have to be real. They're stories for a reason. You can have the wildest names, craziest settings, and they can never actually be unrealistic because in the book world, anything can happen.
That's something I need to remember. I nitpick my stories apart even without rereading what I've written. I know that if I do go back and look when I'm self-doubting, it will all go to waste.
There's millions of things happening at this very moment in time. And again now, and again, and again...Who's to say what happens in your story isn't possible, or isn't already happening? No one. If you want to write a story about horse princesses that live in a castle, go for it - write what makes you happy to be writing.