The poet's task is to create the tree from which such a fruit would fall.
Paul Valéry also describe his perception of first lines so vividly, and to my mind so accurately, that I have never forgotten it: the opening line of a poem, he said, is like finding a fruit on the ground, a piece of fallen fruit you have never seen before, and the poet's task is to create the tree from which such a fruit would fall.
From Mary Ruefle - Madness, Rack and Honey