It's a spectrum. I've always been on the shy side of the spectrum, often times painfully so. I've paid close attention to the development of my 10 grandchildren. All have spent a good deal of time at our house during their early years. Three of them will jump into just about any social situation with both feet. For example when arriving at a busy playground populated by kids they don't know, those three will jump in learn names and join right in, whereas I and the other seven grandchildren would wrap ourselves around mother's legs and never leave her side.

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It can be a birthday party, first day of school, soccer practice, whatever, those three will quickly make friends, while the other always hang back.

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I don't know if it's nature or nurture, but it sure starts young.