How Do You Know When a Poem is Done?

Sometimes I wish writing poetry was like baking. You set the timer, though there are always a few adjustments: slipping a knife into the cake to see if it's still sticky inside, or pressing a fingertip to see if the surface bounces back. At least we know what it's supposed to look and taste like.

Poetry is trickier. Recently I met someone who sent me a poem for my opinion. I told her I liked it, but mentioned a few words and phrases that felt a bit mushy, to continue with the cake metaphor. Th...