So what is happening when we chronically overestimate the odds of success? The Neuroscience of Looking at the Bright Side suggests that in addition to the long known human tendency to discount information that counters a prevailing or optimistic view, we have a lessened future ability to process undesirable information.
How can prediction errors help us to understand optimism? [In one study] participants estimated their likelihood of experiencing 80 negative events including various diseases and criminal acts. They then saw the statistical likelihoods of these events happening to an average person of their age. We then measured how much participants updated their predictions by having them re-estimate their personal likelihoods of experiencing these 80 adverse life events. When given good news -- i.e., a bad outcome is not as likely as you thought -- people responded strongly. But given bad news, they tended to change their prediction only a little bit. Importantly, distinct brain regions seemed to be related to prediction errors for good and bad news about the future. Interestingly, the more optimistic a participant was the less efficiently one of these regions coded for undesirable information. Thus, the bias in how errors are processed in the brain can account for the tendency to maintain rose-colored views (emphasis supplied).
I wonder if the reverse is true - if over-weighting bad information can leave an individual pre-disposed to pass on opportunity (I would suspect it does) and what longitudinal studies, if any, might say about life satisfaction been those who always look on the bright side and those who do not.