Some people can't help being pessimistic, suggests a new study that found the amount of a chemical in the brain affects how we view the world. Levels of a molecule called neuropeptide Y (NPY) directly relate to whether we have a "glass half empty" or "glass half full" attitude. Those with lower levels of the substance are much more negative and less able to deal with stress. They are also more susceptible to depression. The team at University of Michigan believe the amount of NPY in the brain is genetically programmed and hope the discovery could lead to early diagnosis of and prevention of psychiatric illness.