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Pessimism bias is an effect in which people exaggerate the likelihood that negative things will happen to them. It contrasts with optimism bias. The difference is that we are in an improbable way worried about our society's future. Conversely, optimism bias is a tendency to underestimate personal risks and overestimate the likelihood of positive life events.
People with depression are particularly likely to exhibit a pessimism bias. This is likely explained by the fact depressed people think negatively in general. Surveys of smokers have found that their ratings of their risk of heart disease showed a small but significant pessimism bias; however, the literature as a whole is inconclusive.