What makes an introvert?

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Around one in two people are introverts - but it's usually the extroverts who get heard. Introverts need time alone to recharge and space to think. Author J. K. Rowling and Rosa Parks, the civil rights activist, are both cited as this personality type. Lisa Kaenzig, a specialist on education for introverts, explains. Image: A woman hiding her face, Credit: Thinkstock