The composer does not want the self-sufficiency of a richly complex text: he or she wants to feel that the text is something in need of musical setti… - James Fenton

Poetry is not a metrical exercise.

Tennyson follows his feelings in creating each line. He follows the music in his head. If you had asked him, at the end of the day, to describe the prosody of the poem to you, he would no doubt have had to think for a moment before he could answer you, not because he was ignorant of the terms, but because he had been writing a poem, not a metrical exercise. At every point, he was exerting his free will. And the outcome of that exertion was the form.

A serious mistake in a nightie, A grave disappointment all round
Is all that you'll get from th'Almighty, Is all that you'll get underground.
Oh he said: "If you lay off the crumpet
I'll see you alright in the end.
Just hang on until the last trumpet.
Have faith in me, chum – I'm your friend."