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

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.

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

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.

In a typical 401k plan, when you first become eligible you get a big pile of forms and you're told, fill out these forms if you want to join. Tell us how much amount you've saved and how you want to invest the money. In, under automatic enrollment you get that same pile of forms but the top page says, if you don't fill out these forms, we're going to enroll you anyway and we're going to enroll you at this saving rate and in these investments.

"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.

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.