A psychology essay would be usually written by a student specializing in the field of medicine. In some instances, you could be asked to write one to test your analytical skills and knowledge of psychological tendencies in a person. What sets this essay apart is the amount of knowledge you would have to gain before attempting it. Certain inherent qualities help in diagnosing and showing you an approach to a psychological problem. You would have to acquire knowledge suited to write authoritatively on the subject.