I realised that today we are very much interested in reading about subjects that would have also interested people in the 1500s: ghosts, demons and things that go bump in the night.
Once a novel gets going and I know it is viable, I don't then worry about plot or themes. These things will come in almost automatically because the characters are now pulling the story.
You don't have to have magic unicorn powers. You work at it, and you get better. It's like anything: You sit there and do it every day, and eventually you get good at it.