The things that motivate us are to help other people, to feel that we're useful, to feel that we're getting better, to feel that we are kind of living to our potential, to get a sense of meaning. All of those things are positive.

Interesting thing that is happening in American society is that people are starting to talk about money. I don't know how you feel about this, but for a long time, nobody was talking about money. It was a secret. And it's kind of very interesting because we do lots of stuff to portray to people about how much money we have, the clothes we wear and the cars we have and the house - they all kind of depict to other people, signal how much money we make, but we don't talk about it specifically.

But suppose we are nothing more than the sum of our first, naive, random behaviors. What then?

When it comes to the mental world, when we design things like health care and retirement and stock markets, we somehow forget the idea that we are limited. I think that if we understood our cognitive limitations in the same way that we understand our physical limitations … we could design a better world.

There's something about [cyclically] doing something over and over and over that seems to be particularly demotivating.

People are irrational - and predictably so.

What you should do is wait until the end of each month, and then say, "OK, how much money do I have? How much do I need? Let me send the rest to retirement."