But space travel can't ease the pressure on a planet grown too crowded not even with today's ships and probably not with any future ships-because stupid people won't leave the slopes of their home volcano even when it starts to smoke and rumble. What space travel does do is drain off the best brains: those smart enough to see a catastrophe before it happens, and with the guts to pay the price-abandon home, wealth, friends, relatives, everything-and go. That's a tiny fraction of one percent. But that's enough.

Most neuroses and some psychoses can be traced to the unnecessary and unhealthy habit of daily wallowing in the troubles and sins of five billion strangers.

The truth of a proposition has nothing to do with its credibility. And vice versa.

Duty is a debt you owe to yourself to fulfill obligations you have assumed voluntarily.

The lessons of history teach us - if the lessons of history teach us anything - that nobody learns the lessons that history teaches us.

Faith is intellectual laziness.

Being privileged to work hard for long hours at something you think is worth doing is the best kind of play.