Charles Duhigg

There is a woman named Wendy Wood, who did a study when she was at Duke, and she followed around college students to try to figure out how much of their day was decision-making versus how much was habit. And what she found was that about 45 percent of all the behaviors that someone did in a day was habit.

As homeowners see the value of their homes decline, they become more likely to delay purchases of the big items - like automobiles, electronics and home appliances - that are ballasts of the American economy. When those purchases decline, large manufacturing firms, suddenly short on funds, could begin laying off employees.

The lower spreads mean lower costs for investors, because Nasdaq investors generally do not trade directly with one another. Instead, they usually buy and sell from market-makers, brokerage firms that flip shares between buyers and sellers and keep the spread for themselves.