Is it possible to write a well-written fiction book without incorporating themes or focusing on them? If so, how should one go about doing so?

Any story you come up with will have themes, but where most writers focus hard on them before writing the story, I actually tend not to think about themes until they emerge naturally.

To explain, I focus on telling a good, focused story and the characters in it. The themes are basically subconscious for me. And while I'm outlining the story, I'll notice a theme that naturally comes out of character choices and story points and I can develop it naturally.

I think if I personally focused on a theme from the start, the story itself would suffer for it. I'd be writing the story around the theme, rather than writing the story as it should naturally progress and discovering the themes in the outlining process.

I hope that makes sense.