Optimism and the tendency for people to be overly optimistic while ignoring the potential for failure is discussed in this Tali Sharot speech. The cognitive neuroscientist argues that the majority of individuals overestimate the likelihood of experiencing good events while underestimating the possibility of experiencing bad events. This optimistic vs. realistic approach makes for particularly jarring situations when individuals are met with unfavorable outcomes and events.
However, individuals who generally have a more positive approach are happier than people who are constantly pessimistic. Thinking negatively about an outcome so that positive news will be a welcome surprise is not a beneficial attitude.
The key is to balance the positives of having an encouraging opinion about oneself without ignoring the realities of possible setbacks and obstacles.