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

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.

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.

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

Everyone's lost a lot of money on their 401k plans. I've heard some people calling them 201k plans. So it's even more important to get people to be saving more for retirement. Behavioral economics has helped us learn a lot about how to do that.

If rather than setting the minimum balance as the lowest possible amount, so we keep people in debt for as long as possible, we raise the minimum payment and encourage people to pay off their credit cards, we're going to make less money, but we're going to have costumers that are more solvent.

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.