I'm not really sure what Millay meant by this poem, but it has alway made me think of artists.
Excerpted from How Naked, How Without a Wall:
The man who ventures forth alone
When other men are snug within,
Walks on his marrow, not his bone,
And lacks his outer skin.
The draughty caverns of his breath
Grow visible, heart shines through:
Surely a thin which only death
Can have a right to do.
--by Edna St. Vincent Millay, Wine From These Grapes