Alina Tugend offers a nice overview of recent research on optimism and pessimism. The verdict? "... Moderate optimism may be good for you, extreme optimism is not. And at times some pessimism is helpful."
Here's how the moderates deal with life:
Moderate optimists, on the other hand, work longer hours, save more money, are more likely to pay off their credit card balances and believe their income will grow over the next five years.
How about the extremes?
“Extreme optimists don’t think savings are good, don’t pay off their credit cards and don’t do long-term planning,” Professor Puri said. “They think the economy will always do better.”
They are also more likely to remarry if divorced. [Bold emphasis added]