Our brains have an "optimism bias"
based on study in Nature Neuroscience by Tali Sharot, University College London .."clues to the brain's predilection to the positive, identifying regions that may fuel this "optimism bias." by preferentially responding to rosier information
[the study involved 19 individuals... 79% of them paid more attention when the news (related to predicting chances of something bad happening) turned out to be better than they had predicted. They received this "better than anticipated" info prefrontal cortext, where conscious reasoning takes place. Whereas the" right inferior frontal gyrus" changed in response to discouraging information." But this activity "did not correspond as closely with the magnitude of error in the participants initial risk estimates." this inconsistency has been "most clearly or most often" for people who score higher for optimism. "This study jibes with past studies that observed an "optimism bias" in about 80 percent of the population.
Andrea Anderson, "Unflagging Optimism," Scientific American Mind, March-April, 2012, 11.