In the poem, the unopened flower symbolizes the possibility that can be harbored by a human being as well as by time. In this way, the speaker recognizes the beauty of a flower and the sense of possibility it represents. However, because of the speaker's pessimism and hopelessness, he feels that all possibility has been lost, and so "the flower closes like a fist."
A simile -- a comparison made in literature by comparing two unrelated things by using "like" or "as" -- is a tool for expressing imagery in poetry. Similes serve to enrich the meaning of one thing by relating it to the meaning and connotations surrounding another thing. In the poem, Fenton writes that a flower "opened like a crimson hand" and later that it "closes like a fist." A hand implies tenderness, offering, strength and touch; all these qualities are imbued in the flower through simile.
"The Possibility" uses personification -- giving human characteristics to non-human things -- to convey the speaker's depressed tone. Fenton writes that "the jays are swearing in the wood" rather than singing or calling to one another. By giving the birds such an angry and aggressive human quality, the speaker gives the surrounding natural environment a sense of gloom and negativity that reflects his sense of lost possibility. He also says that the "lizard on the wall" and the "sudden silence from the wood" tell him that he no longer possesses the ability to be good. This use of personification communicates the speaker's overwhelming sense of sadness that he feels all around him.
Some of the themes contained in the poem include pessimism -- the ways people react to obstacles and hardship, depression, losing confidence and losing inspiration. For example, the speaker says that in the past, "I was sure that I was strong." Now he has lost his confidence in himself and in his possibility to be strong, productive and good. The speaker also says that despite knowing that flowers are beautiful, he cannot get himself to recognize or be moved by their beauty: "I know this flower is beautiful...It was not beautiful to me." This communicates the theme of depression, whether temporary or clinical, and the cost of this condition on how a person views and identifies the possibilities offered to them in the world.