When an economist says the evidence is "mixed," he or she means that theory says one thing and data says the opposite.

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.

The assumption that everybody will figure out how much they have to save and then will just implement that plan is obviously preposterous.

The same with the mortgage brokers that were selling people mortgages they couldn't afford. We shouldn't pay them on each mortgage they write. They should have what they call "skin in the game," where they've got to reimburse us if the guy who sold the mortgage defaults.

"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.

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

The lesson from behavioral economics is that people only save if it's automatic.