Optimist (well, sometimes - I can be in an equally pessimistic mood) checking in...
Where the actual probability of a bad thing happening is higher than the person guessed - and they still don't adjust the belief in the likelihood of this happening to them, personally -- I think this "glitch" is due to the ability some people have of believing "that won't happen to me". Sort of a hold-over from the adolescent belief in invincability/risk-taking. A belief that one is the exception to the rule (or really, really "special").
Now, what I'd like to see - though I don't think I could design the experiment/study - is a measure of how that turned out for the same group of people, over time. How many had their cars stolen? How many didn't? Because then, the next study could also look at how the initial optimism - and sheer luck - reinforced the uncorrect belief of being an exception to the statistics. Or not. Would people change or moderate their scores on a scale of total optimism to total pessimism?
But let's say one scored heavily toward the pessimistic side. What is the change in belief (and overall attitude, over time) with the statistical evidence that (some) bad things really happen less often than one believes? The parts of our brains that mis-recognizes a stick for a snake, will stand down from the adrenalin rush this time... but WON'T ignore other sticks, in other situations that are snaky suspects. That association and response pattern remains. It's the bio-survival instinct... would we say that's more realistic? can it even be qualified as either optimistic or pessimistic?
So, nature vs nurture... I think it would be really hard to separate out the "nature" tendencies, because of how much impact repetition, intense emotional experience, education and prevailing social attitudes - that comes from the whole category defined as nurture - has on a person. I would propose that life experiences could actually turn a "natural" optimist into a raving pessimist... so in the lovely, perfect world of theory... it should be possible to change a pessimist into an optimist. But I believe I've read recently that there isn't any really good reason - no return on investment - for trying to change from one to the other. That optimists aren't really what we'd call "happier" or more content than pessimists. That generalization, probably applies only to the people in the middle of the range... while people at one extreme or the other, my guess, would be both be equally unhappy.
The optimist because life doesn't live up to those extremely high expectations. But the extreme optimist doesn't let go of the expectation after disappointment; the perception that all those happy things will eventually "come to pass" lives on, altered perhaps... but it's still there. Rationalization and self-soothing would be this optimist's best tools.
The pessimist would be equally unhappy, because of the PERCEPTION of being surrounded by affirmations, that life sucks. That stick-snake connection would keep someone jumpy too, wouldn't it? (Altho' they might actually experience a perverse satisfaction that - YEP; they were right this time.) And yes, an extreme pessimist can make even birthday cake seem like an evil plot... something life threatening, too.
Much as neuroscience and the ability to now track activity in the brain intrigues me, I still agree with tt that there is much about life and humans that's unknowable with any real certainty. And like FW, I'd much prefer to rely on someone who's more realistic about the risks involved in an undertaking, than someone who's too preternaturally optimistic.... as long as that risk assessment didn't simply paralyze me and set up additional obstacles to really living life. The mythical "middle way", in other words... which is almost never exactly in the middle... it wanders... just like me! LOL...