We need to be aware of our natural born optimism, for that harms good decision making, too. The neuroscientist Tali Sharot conducted a study in which she asked volunteers what they believed the chances were of various unpleasant events’ occurring — events like being robbed or developing Parkinson’s disease. She then told them what the real chances of such an event happening actually were. What she discovered was fascinating. When the volunteers were given information that was better than they hoped or expected — say, for example, that the risk of complications in surgery was only 10 percent when they thought it was 30 percent — they adjusted closer to the new risk percentages presented. But if it was worse, they tended to ignore this new information.
This could explain why smokers often persist with smoking despite the overwhelming evidence that it’s bad for them. If their unconscious belief is that they won’t get lung cancer, for every warning from an antismoking campaigner, their brain is giving a lot more weight to that story of the 99-year-old lady who smokes 50 cigarettes a day but is still going strong.