Narcissism, like the other personality disorders, is a condition that's known as ego-syntonic. In other words, the paranoid person really does believe that people are after him, and the narcissist really does believe that he or she is better than or more entitled than other people, and truly doesn't see why that's not the case.

Identical twins are ideal lab specimens for studying the difference between learned and inherited traits since they come from the womb preloaded with matching genetic operating systems. Any meaningful differences in their behaviors or personalities are thus likely to have been acquired, not innate.

Certainly, people can get along without siblings. Single children do, and there are people who have irreparably estranged relationships with their siblings who live full and satisfying lives, but to have siblings and not make the most of that resource is squandering one of the greatest interpersonal resources you'll ever have.

All behavioral or mood disorders - including depression, OCD, ADHD and addiction - have some neurochemical components, but sufferers can still work to overcome them.

It's far too much to say that effective hoping is the only - or even the biggest - part of what it takes to succeed. If 14% of business productivity can be attributed to hope, that means 86% is dependent on raw talent, fickle business cycles, the quality of the product you're selling, and often pure, dumb luck.

Introverts listen better, they assess risks more carefully, they can be wiser managers. It's not for nothing that the Silicon Valley billionaires are so often the retiring types.

I was born in the U.S., my wife was born in Mexico and emigrated here when she was in college, and my daughters were born in New York City. That makes them passport-carrying, natural-born, eligible-to-run-for-president Americans. But they're also Mexicans and they like that just fine.