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.

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.

Older siblings get more total-immersion mentoring with their parents before younger siblings come along. As a result, they get an IQ and linguistic advantage because they are the exclusive focus of their parents' attention.

At the root of the shy temperament is a deep fear of social judgment, one so severe it can sometimes be crippling. Introverted people don't worry unduly about whether they'll be found wanting, they just find too much socializing exhausting and would prefer either to be alone or in the company of a select few people.

When you're your parents' one shot at a genetic legacy, you may get to attend all the best schools, wear all the best clothes and eat all the best foods - at least relative to children in multiple-sibling households. But you also wind up with an overweening sense of your own importance.

As the National Football League and other pro sports increasingly reckon with the early dementia, mental health issues, suicides and even criminal behavior of former players, the risk of what's known as chronic traumatic encephalopathy (CTE), is becoming clear.

Psychopaths know the technical difference between right and wrong - which is one of the reasons their insanity pleas in criminal cases so rarely succeed; they just fail to act on that knowledge.