In the poem "Last Answers", Carl Sandburg ruminates about the essence of all things.  His thinking is instigated when a woman asks him what the meaning is of a poem he has written about the mist.  The poem in question had apparently been an appreciation of

"the beauty of mist, how pearl and gray of it mix and reel, and change the drab shanties with lighted lamps at evening into points of mystery quivering with color".

In writing his poem originally, Sandburg had addressed the beauty of mist as a part of nature, and he had tried to highlight its loveliness in a physical, especially visual, sense.  Upon further reflection, however, he realizes that mist has much more significance than its ability to please the eye.  It is the essence of all life, and all being; it is the raw material of the universe, like dust.  Sandburg says that

"The whole world was mist once long ago and some day it will all go back to mist...our skulls and lungs are more water than bone and tissue".

When the entities of the natural world are broken down to their smallest components, everything goes "running back to dust and mist".  According to Sandburg, "all poets love dust and mist" because ultimately, everything is made out of these two things; "all the last answers go running back to dust and mist".