Where do the things I dream about come from?

Am I alone in this, why do any topic I focus on including those observed briefly end up as themes in my dream? The other day I was watching talk show where the host and guest were talking about taking a jet to Vegas. When I went to sleep, I dreamt that I was taking a Jet plane to England and en route, we did a scenic tour of New York City. Just to let you know early that day I had spoken to my cousin in England and whiles watching a television show based in New York City, I commented that I love to see my favorite New York sights on television.