A good rule of thumb is to assume that everything matters.

People exaggerate their own skills. they are optimistic about their prospects and overconfident about their guesses, including which managers to pick.

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

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.

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.

The reason is they failed to learned the primary lesson we should have learned from when Long Term Capital Management went belly up ten years ago. That is, investments that seem uncorrelated can be correlated simply because we're interested in it.

Retirement savings is probably behavioral economists' greatest success story. It is a prototypical behavioral-economics problem because saving for retirement is cognitively hard - figuring out how much to save - and requires self-control.