I believe in everything until it's disproved. So I believe in fairies, the myths, dragons. It all exists, even if it's in your mind. Who's to say that dreams and nightmares aren't as real as the here and now?

This quote is saying that people should approach the world with an open mind. We shouldn’t rule out things like fairies, dragons and other myths as they could be real, even if they only exist in our imagination. Dreams and nightmares could be as real as the present day world, so don’t discount them. The quote is saying that we shouldn’t be so quick to dismiss things, until we can prove that they are not real.