Usually the poems are written in one sitting. There's always a groping towards some satisfying ending. But I'd say the hardest part is not writing. Once the writing starts, it's too pleasurable to think of it as a difficulty.
Billy CollinsI'm very conscious of the fact that every line should have a cadence to it. It should contribute to the progress of the poem. And that the ending of the line is a way of turning the reader's attention back into the interior of the poem.
Billy Collins