From The Wall Street Journal's review of a JFE paper:
Optimists, the Duke finance scholars discovered, worked longer hours every week, expected to retire later in life, were less likely to smoke and, when they divorced, were more likely to remarry. They also saved more, had more of their wealth in liquid assets, invested more in individual stocks and paid credit-card bills more promptly.
Yet those who saw the future too brightly...behaved in just the opposite way...Rather than save, they squandered. They postponed bill-paying. Instead of taking the long view, they barely looked past tomorrow. Statistically, they were more likely to be day traders. "Optimism is a little like red wine," said Duke finance professor and study co-author Manju Puri. "In moderation, it is good for you; but no one would suggest you drink two bottles a day."