Robert Frost says

A poem is never a put-up job so to speak. It begins as a lump in the throat, a sense of wrong, a homesickness, a lovesickness. It is a reaching-out toward expression; an effort to find fulfillment. A complete poem is one where an emotion finds the thought and the thought finds the words. It is never a thought to begin with. It is at its best when it is a tantalizing vagueness. It finds its thought and succeeds, or doesn't find it and comes to nothing. It finds its thought or makes its thought. I suppose it finds it lying around with others not so much to its purpose in a more or less full mind. That's why it oftener comes to nothing in youth before experience has filled the mind with thoughts. It may be a big big emotion then and yet finds nothing it can embody in.…

There are only three things, after all, that a poem must reach: the eye, the ear, and what we may call the heart or the mind. It is the most important of all to reach the heart of the reader. And the surest way to reach the heart is through the ear. The visual images thrown up by a poem are important, but it is more important still to choose and arrange words in a sequence so as virtually to control the intonations and pauses of the reader's voice. By the arrangement and choice of words on the part of the poet, the effects of humor, pathos, hysteria, anger, and in fact, all effects, can be indicated or obtained.