There is no question here, However that is true.
I feel that the missing word is most likely "lens" - check if it's among your options.
When something is compared to a lens through which the word is seen, it means that the world is seen through a certain perspective, that it's using a certain interpretation: here that of literary theory.
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1. The speaker wants the rest of the world to acknowledge and reflect the magnitude of the speaker's loss. The poem thus suggests that, whether you've lost a loved one or had your heartbroken, part of what makes grief so terrible, so hard to endure, is the isolation it creates.
