Explain what elements prevented the use of the commonplace from simply resulting in poetry that is dull and boring.

There were/are many elements that prevented the use of 'commonplace' from simply resulting in poetry that was/is dull and boring. The majority of commonplace writing consisted of  poets picking common objects yes, but using them in a way that everyone could relate to these objects. They took the ordinary and made something out of it. The purpose really was to illustrate  that even in the most common things we can find creativity. This concept is what is called defamiliarization or ostranenie.

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It shows that the milk is like life to the boy