Philosophers call this the “paradox of tragedy,” and they’ve puzzled over it for centuries. Why do we sometimes welcome sorrow, when the rest of the … - Susan Cain

(Finland is a famously introverted nation. Finnish joke: How can you tell if a Finn likes you? He's staring at your shoes instead of his own.)

...the results have consistently suggested that introversion and extroversion, like other major personality traits such as agreeableness and conscientiousness, are about 40 to 50 percent heritable.

For example, highly sensitive people tend to be keen observers who look before they leap. They arrange their lives in ways that limit surprises. They're often sensitive to sights, sounds, smells, pain, coffee. They have difficulty when being observed (at work, say, or performing at a music recital) or judged for general worthiness (dating, job interviews). But there are new insights. The highly sensitive tend to be philosophical or spiritual in their orientation, rather than materialistic or hedonistic. They dislike small talk. They often describe themselves as creative or intuitive (just as Aron's husband had described her). They dream vividly, and can often recall their dreams the next day. They love music, nature, art, physical beauty. They feel exceptionally strong emotions — sometimes acute bouts of joy, but also sorrow, melancholy, and fear. Highly sensitive people also process information about their environments — both physical and emotional — unusually deeply. They tend to notice subtleties that others miss — another person's shift in mood, say, or a lightbulb burning a touch too brightly.