So the world is much more correlated than we give credit to. And so we see more of what Nassim Taleb calls "black swan events" - rare events happen more often than they should because the world is more correlated.

"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.

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.

It turns out, that men, when they're taking care of their business, they're not fully attending to the task at hand, but, I'm sure there's an evolutionary explanation for this, if you give them a target, they will aim.

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.

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.

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."