If you're an older sibling and you have a younger sibling who needs mentoring or is afraid of the dark, you develop nurturing and empathic skills that you wouldn't otherwise have.

Since narcissism is fueled by a greater need to be admired than to be liked, psychologists might use that fact as a therapeutic lever - stressing to patients that being known as a narcissist will actually cause them to lose the respect and social status they crave.

No one ever pretended that shopping for anything is a rational experience. If it were, would there be Fluffernutter? Laceless sneakers? Porkpie hats? Would the Chia Pet even exist?

There's only one thing harder than living in a home with an adolescent - and that's being an adolescent. The moodiness, the volatility, the wholesale lack of impulse control, all would be close to clinical conditions if they occurred at another point in life. In adolescence, they're just part of the behavioral portfolio.

My own life has in some ways been a decades-long tour of the sibling experience. I have full sibs, I have half-sibs, and for a time I had step-sibs.

We're learning how important it is both to preserve sibling relationships if they work and repair them if they're broken. We're also learning a lot about nonliteral siblings - stepsiblings, half-siblings - and the surprising power they can have.

It's one of the worst-kept secrets of family life that all parents have a preferred son or daughter, and the rules for acknowledging it are the same everywhere: The favored kids recognize their status and keep quiet about it - the better to preserve the good thing they've got going and to keep their siblings off their back.