I was working on a story the other day and thought I had a theme in it which was in some of my other stories. I never plan on themes when I'm writing, but somehow they creep through. It seems to me what we learn and experience through life, our lessons learned, become our beliefs and account for our themes in the stories. Romance stories have an overall theme about the power of love, but as we write, our characters show us their natures, beliefs and views on life. This might reflect our own or in some of the characters may be the direct opposite. Think I'll look for themes now when I write something.