What a question for the mind to chew on! I don't believe there is a correct answer on your question, but that's the best part...in my humble opinion.
I tend to think we are dreamers by design, likely because my dreams are quite vivid and tend to have a life of their own. They are like a continuous story...which then brings me to...destiny or fate, because of the theory of "Indra's Web" where everything is connected to everything...thus premonition type dreams, or dreams powerful and persistent in nature.
It likely varies per individual, much like so many other unexplained things in life.