Rip Van Winkle would be the ideal stock market investor: Rip could invest in the market before his nap and when he woke up 20 years later, he'd be happy. He would have been asleep through all the ups and downs in between. But few investors resemble Mr. Van Winkle. The more often an investor counts his money - or looks at the value of his mutual funds in the newspaper - the lower his risk tolerance.

A company invites their employees to sign up for a plan where every time they get a raise, some part of that raise goes to increasing their contribution rate to the 401k plan. In the first company we convinced to adopt this plan, saving rates tripled.

There's a second component of a good savings plan, which is something that a colleague of mine called Schlomo Benartzi and I developed many years ago, that we call "save more tomorrow."

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.

When should we nudge and when should we shove, I think, it's a political judgment. Obviously in some situations we need shoves, we need laws. Fraud is against the law, murder is against the law, drunk-driving is against the law. We don't need just nudges.

he card companies will often, as a courtesy, honor that credit card, but hit you with a penalty. And you keep swiping your card for $3 at Starbucks for your latté, and you're getting hit with a $25 penalty because it's over your credit limit.