Taste.

I have found that if you let a poem sit around long enough, you come to see and hear it better. Not that a poem in progress doesn't reach a point of being pretty much finished. So I don't rush it — it's a matter of allowing intuition and taste to come into play; you choose to hold on to a piece, waiting for some little turn of insight. This is true of prose writing, too. But letting it wait might be a kind of luxury sometimes because there are often urgent reasons to get things into the world, especially essays dealing with current issues. I recently finished a project I called Mountains and Rivers Without End — a series of longish poems that I have been working at for decades. And I'm glad I let it wait that long, it is more tasty.

Gary Snyder