Who do You Write For?

I was asked this the other day. It stopped me. I didn't know.
Yet this is a very important question for a writer. It determines how you write your book or article or poem or essay. It affects the point of view and vocabulary.
Who do I write for? How do you know?
I thought about where some of my book ideas come from, the subjects I like writing about, and what I consider when I write.
It turns out I write primarily for me. My ideas are things that interest me. My subjects are things that pique my interest. My considerations are what I want to know about.
Is this a bad thing?
It does limit my audience to people curious about and interested in the things I am interested in. That could be bad.
Being interested and excited by the subjects I am writing about can add spice to my writing. This is a good thing.
Perhaps I should write for me and edit for an intended audience. Is this possible? I don't know. I think I'll try.