I'm a mathematician and a writer. It sometimes occurs to me that both of these things are sort of like being God.
In maths, you get to say 'Let there be...' and there is, Old Testament style, which feels awesome.
And unlike every other branch of science, maths is Bottom Up. Other sciences are Top Down: you look at the world and try to work out how it fits together and does what it does. In maths, you start from the very building blocks and find out what you can do with them. It's as if a physicist started with the idea of quarks (or whatever they are made up of, if they aren't as small as you can go), and deciphered how atoms and molecules and everything bigger worked from there. Which is presumably what God does, if there is a God (I believe there is, but I have absolutely no problem with it if you don't).
This means that you can prove things in maths: unlike in other sciences where the best you can get is a theory (that is, a comprehensive explanation supported by a great deal of evidence) that is the best explanation anyone can find and fits all the evidence is the nearest you can get to proof, and still could, potentially, turn out to be wrong, in maths you can prove things, and then you can be 100% certain that it's not possible for it to be otherwise.
As for being a writer: I create worlds, and people to fill them.
I put a great deal of effort into it, and make sure that things work - you already know about my scientifically plausible vampires, and just recently I've been looking up pterosaurs to design a basilisk, which in my version is a giant flying snake-creature, for another story - and my characters are all created, to some extent, in my image, because it's not really possible to make someone up without putting some of yourself into them.
And you know, I do seriously wonder sometimes if my creations are real to themselves: I don't see why not as they're pretty real to me. And then I wonder if it's wrong of me to put them through all the things I do, although it's not really possible not to: you can't have a story without conflict, and you can't have conflict without suffering. And stories have a mind of their own, so if they decide on one route, you can either follow, no matter the consequences, or abandon it entirely.
of course that leads to the question: if God is an author, does that make Christianity the biggest work of self-insert fiction ever?