Does the exclusion of poetic vocabulary imply that only colloquial language is allowed, that I must imagine someone actually saying the words out loud? No. Words from non-colloquial registers would be admissable. Generally speaking, a lot of bad poetry could be eliminated simply by excluding anything you couldn't imagine anyone ever saying, but that would take a lot of great poetry out of the picture as well. And a lot in the middle!

When you ask a person who apparently knows nothing at all about poetry to write a poem, the results will sound like a poem. That means that the non-poet type person actually already has a poetic template in place. To learn to write the person must unlearn this set of assumptions.

The next step for most people is to learn a sort of period style. In effect, they eliminate the popular-based template ("the dark storms of my heart") and learn to write plain-spoken autobiographical lyrics in loose free verse (for example). Much of what goes on in writing workshops is the unlearning of a popular template and the substitution of a different sort of poetic diction.

This new template too must be unlearned. The process will never come to an end, however, since any style is susceptible to being transformed itself into a "poetic" diction. It follows that learning to write poetry is a process of unlearning.