Credit cards have been extremely profitable to banks. They're profitable not from the fees they collect from the retailers that use the credit cards, that pays the bills, but the real profits come from the interest payments and the charges to users that are unexpected.

Most economists, including me, agree that longevity insurance would make sense for a lot of people.

Most people start claiming benefits within a year of when they become eligible, although benefits increase substantially if they wait.

"Save more tomorrow" is a nudge to help people do what they know they want to do, which is save more, but they can't bring themselves to save more now. Just like many of us are planning to go on diets next month, or maybe in two months, certainly not tonight.

Every American worker should be able to save for retirement via payroll deductions.

LTCM lost money when Russia defaulted on a certain class of bonds, and then they had other investments like on the spread between two different kinds of shares of Royal Dutch Shell Oil Company. Now that seems completely unrelated to Russian bonds. But they were related because other hedge funds saw similar discrepancies and they were all making similar bets.

Retirement savings is probably behavioral economists' greatest success story. It is a prototypical behavioral-economics problem because saving for retirement is cognitively hard - figuring out how much to save - and requires self-control.