There's a tendency to think of art as something others do. Art is mysterious; it comes from a magical place. It's not like going to a day job and pumping out widgets or code or happy customers—all the things you and your ordinary friends produce.
Maybe that's why it's always slightly uncomfortable when good friends create good things. When watching a friend's band, or play, or art show, it may be objectively fantastic, but that's weird, because fantastic acts of creation shouldn't come from the real person you've known for years. They should come from an other.
We've even invented the concept of a muse: an other—real or imaginary—who provides the source of artistic inspiration. No way, it couldn't be a regular person's brain coming up with this stuff. It must originate somewhere else.
It's all bullshit, of course. Art is a result of regular brains and regular hands put to hard work. But the belief persists, for some reason.
I try to be aware of this. As a writer, and a writer of horror, the creepiest art of all, I am conscious of how strange it can be for people around me. Self promotion is uncomfortable, partially for that reason. I'd almost prefer to stand up on a stage and talk about my book to a crowd of strangers—to whom I am an other—than post about it on Facebook.
P.S. Buy my book.