My bed is like a little boat; Nurse helps me in when I embark; She girds me in my sailor's coat And starts me in the dark. At night I go on board and say Good-night to all my friends on shore; I shut my eyes and sail away And see and hear no more. And sometimes things to bed I take, As prudent sailors have to do; Perhaps a slice of wedding-cake, Perhaps a toy or two. All night across the dark we steer; But when the day returns at last, Safe in my room beside the pier, I find my vessel fast. In the first stanza of the poem, why does the speaker say the nurse "starts me in the dark"?