The writer must know his readers...their hearts and dreams.
Debbie's thoughts:
By tapping into those desires and dreams, the writer can capture the reader's interest: his desire to see justice done, his longing to feel he can control of life in some small way even when it seems out of control, etc. The more the characters struggle with problems that everyone struggles with, the more the reader can relate to the problems and will read on to see how the hero deals with them.
Likewise, the most effective horror stories tap into the things we all fear: the unknown, loss of control, etc.