Publishers, naturally, loathe used books and have developed strategies to depress the secondhand market. They bring out new, even more expensive editions of popular textbooks every three to four years, in a classic cycle of planned obsolescence.

The smartest groups, then, are made up of people with diverse perspectives who are able to stay independent of each other.

Unlike most government programs, Social Security and, in part, Medicare are funded by payroll taxes dedicated specifically to them. Some of the tax revenue pays for current benefits; anything that's left over goes into trust funds for the future. The programs were designed this way for political reasons.

It's a familiar truism that at any one moment, financial markets are dominated by either fear or greed. But the healthiest markets are those that are animated by both fear and greed at the same time.

Technology is supposed to make our lives easier, allowing us to do things more quickly and efficiently. But too often it seems to make things harder, leaving us with fifty-button remote controls, digital cameras with hundreds of mysterious features and book-length manuals, and cars with dashboard systems worthy of the space shuttle.

A long-term crisis, after a certain point, no longer seems like a crisis. It seems like the way things are.

The financial crisis of 2008 was not caused by investment banks betting against the housing market in 2007. It was caused by the fact that too few investors - including all of the big investment banks - bet too heavily on the housing market in the years before 2007.