So, what's a nudge? A nudge is some small feature of the environment that attracts our attention and alters our behavior.

If people just put away what's left at the end of the month, that's a recipe for failure.

Maybe you'll take the cash out. So a credit card company or a bank that goes into the business of saying we're going to be the broker, we're going to sell you a mortgage that you're going to be able to pay off, we're going to help you reduce your credit card debt, we're going to help you save for retirement, we're going to put you into mutual funds that have low fees rather than high fees.

Why tie to gold? Why not 1982 Bordeaux?

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.

I think one lesson we have to learn is that there's a lot more risk than we're giving credit to, a lot more what economist calls systematic risk.

Recall that people like to do what most people think it is right to do; recall too that people like to do what most people actually do.