<u>Things in life are not as they seem</u> is the best expression of the theme in this passage.
Explanation:
Richard Cory seems to live a very good life because of his riches and adoration by the people. However it is seen in the last sentence that he must have been unhappy with his life and decided to "put a bullet through his head."
people are usaly drawn to first hand account things because it gives them a better understanding of what the person is feeling, or how the setting looks.
