A reader should never be fully able to predict what will happen next. Otherwise, why bother to read the whole poem? The shiver down the spine that an effective poem evokes comes not only from the images, ideas, and emotions it embodies, but also from the freshness of language, apt undercurrents of rhythm, or little unexpected variations in sentence pattern. The fun is never being certain what will pop up—even in something as normally predictable as a refrain. One way or another, it’s good to keep readers on the edge of their chair, alert and interested.