No aspect of a poem is more singular, more unique, than its rhythm. - Robert Pinsky

I think what holds a poem like this together for me, if it’s held together, is largely meter; this one is in iambic pentameter and iambic pentameter whatever else it is, can be a very good glue. It is a very good way to hold things together. It’s like 4:4 you know.

The poet is a particular kind of expert.

There are no rules. However, principles may be discerned in actual practice; for example, in the way people actually speak, or in the lines the poets have written.