There has been an academic debate going on between psychologists since Shelly Taylor published Positive Illusions asserting that the normal mentally healthy person holds on to optimistic illusions. Are most humans not realistic in their view of themselves and the their future? According to psychologists Shelly Taylor and Jonathon Brown:
“One dilemma that immediately arises is that, as noted earlier, many formal definitions of mental health incorporate accurate self-perceptions as one criterion. In establishing criteria for mental health, then, we must subtract this particular one.”
There has been some pushback to asserting that a realistic view of one’s self is not a basis of mental health. Critics have contended that this research showing that the normal person perceives themselves as better than average in ability and future outlook was a result of using an elite population, namely students in prestigious private universities, to conduct research. 
However, others such as neuroscientist Tali Sharot, concur with Shelly and Brown. Sharot has summarized research on this topic in her easy to read books (such as The Science of Optimism – Why We’re Hard –Wired for Hope) aimed at the general public. In her attempt to answer the question why the majority of humans have a built in tendency to be more optimistic than realistic, Sharot claim that optimism is adaptive. In others words, a rosy view of the world makes it easier for a human to survive and reproduce. Much of her theory is based on research showing that people that believe they can overcome a life threatening illness against the odds, such as cancer, are more likely to do so. 
Does unrealistic optimism really provide an advantage, or is it simply a popular idea to sell books? Let’s look at the major advantage optimism is supposed to provide. According to Sharot, low expectations are not a good idea because those with great hopes for the future will keep trying despite setbacks due to the belief that they will be successful, while pessimists will simply give up.
A study by Charles S. Carver et al also asserted that:
“…People who are confident about eventual success continue trying, even when the going is hard. People who are doubtful try to escape the adversity by wishful thinking, they are drawn into temporary distractions that don’t help solve the problem, and they sometimes even stop trying.
It sounds logical, but you must remember that the reason Taylor saw optimism as an illusion is that the majority of people have far less control over events than really exists. They predict outcomes better than actually occur. Personally, I would also like to know how to distinguish the difference between unrealistic optimism and wishful thinking? The two terms seem very similar in my mind.
Carver’s research indicated that although optimism was considered a personality trait, it sometimes was not very stable. In a study that measured the optimism of students in law school to determine this would affect success in their careers (as measured by how much money they made) researchers found that:
“the change in that study was mainly in the optimistic direction and was predicted by increases in social resource.”
In other words as former students climbed up the socio-economic ladder, they became more optimistic. So again optimism is shown as increasing in a study done among an elite group, students in law school.
However according to Sharot it is all really based on point of view.
“Research shows that whatever the outcome, whether we succeed or we fail, people with high expectations tend to feel better. At the end of the day, how we feel when we get dumped or win an award depends mostly on how we interpret the event.”
So is it simply a matter that optimists are happier with their circumstances? Or is it more closely related to the socio-economic standing which would fit the profile of most students in elite universities and law schools. We really need to measure if optimism rises and falls in cycles that mirror economic growth? If research on optimism continues to be done mainly on populations that are likely to succeed because they already have an advantage we will never know.
 Taylor, S. E. & Brown, J. D. (1988). Illusion and well-being: A social psychological perspective on mental health. , American Psychological Association, Psychological Bulletin, 103, 193—210.
 Colvin C.R., Block J. Do positive illusions foster mental health? An examination of the Taylor and Brown formulation. Psychology Bulletin. 1994 Jul;116 (1):3-20.
 Sharot, T., The Science of Optimism – Why We’re Hard –Wired for Hope
 Carver, Charles S., Michael F. Scheier and Suzanne C. Segerstrom. 2010. “Optimism.” Clinical Psychology Review 30:879-89.
 Sharot, T. The Science of Optimism – Why We’re Hard –Wired for Hope