The 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 a good poem evokes comes from the constant freshness of the language, the apt undercurrents of rhythm, and the little unexpected variations in sentence pattern. The fun is never being certain what will pop up next—even in something as normally predictable as a refrain. One way or another, it’s good to keep your reader on the edge of her chair, alert and interested.