What are the motifs in The Triggering Town: Lectures and Essays on Poetry and Writing by Richard Hugo?

Hugo writes much about how a poet should and shouldn't begin a poem. He speaks of a triggering subject, which is basically a place for a poet to start. However, the poet should not feel bound to this subject throughout the entire poem. The poet should feel free to move to poem as far away from this subject as his emotions prompt him. This triggering subject is basically an idea that gets the poet's thoughts and emotions flowing.