The poem's purpose demonstrates how being childish is dearly miss when you're grown up. In the poem, Shakespeare uses poetic devices, like "night's bright" and "darkly bright", in other words, saying that his dreams are the only place in which he can re image his childhood, rather than the dark light he see being a adult.The most solid evidence we see is "All days are nights to see till I see thee, / And nights bright days when dreams do show thee me.", meaning that the poet feels lonesome in his life, rather than how he felt being a child.