(This is the first of four condensed excerpts from Daniel Kahneman's new book, Thinking Fast and Slow.)

(Bloomberg News) Most of us view the world as more benign than it really is, our own attributes as more favorable than they truly are, and the goals we adopt as more achievable than they are likely to be. We also tend to exaggerate our ability to forecast the future, which fosters overconfidence.

In terms of its consequences for decisions, the optimistic bias may well be the most significant cognitive bias. Because optimistic bias is both a blessing and a risk, you should be both happy and wary if you are temperamentally optimistic.

Optimism is normal, but some fortunate people are more optimistic than the rest of us. If you are genetically endowed with an optimistic bias, you hardly need to be told that you are a lucky person -- you already feel fortunate.

Optimistic people play a disproportionate role in shaping our lives. Their decisions make a difference; they are inventors, entrepreneurs, political and military leaders -- not average people. They got to where they are by seeking challenges and taking risks. They are talented and they have been lucky, almost certainly luckier than they acknowledge.

A survey of founders of small businesses concluded that entrepreneurs are more sanguine than midlevel managers about life in general. Their experiences of success have confirmed their faith in their judgment and in their ability to control events. Their self-confidence is reinforced by the admiration of others. This reasoning leads to a hypothesis: The people who have the greatest influence on the lives of others are likely to be optimistic and overconfident, and to take more risks than they realize.

Optimistic Bias

The evidence suggests that an optimistic bias plays a role -- sometimes the dominant role -- whenever people or institutions voluntarily take on significant risks. More often than not, risk-takers underestimate the odds they face and, because they misread the risks, optimistic entrepreneurs often believe they are prudent, even when they are not. Their confidence sustains a positive mood that helps them obtain resources from others, raise the morale of their employees and enhance their prospects of prevailing. When action is needed, optimism, even of the mildly delusional variety, may be a good thing.

An optimistic temperament encourages persistence in the face of obstacles. But this persistence can be costly. A series of studies by Thomas Astebro shed light on what happens when optimists get bad news. (His data came from Canada's Inventor's Assistance Program -- which provides inventors with objective assessments of the commercial prospects of their ideas. The forecasts of failure in this program are remarkably accurate.)

In Astebro's studies, discouraging news led about half of the inventors to quit after receiving a grade that unequivocally predicted failure. However, 47 percent of them continued development efforts even after being told that their project was hopeless, and on average these individuals doubled their initial losses before giving up.

Significantly, persistence after discouraging advice was relatively common among inventors who had a high score on a personality measure of optimism. This evidence suggests that optimism is widespread, stubborn and costly.