Why are some people "loners"?

Varies: Many of us -- myself included -- enjoy work and play without a lot of other people necessarily being around. Einstein called himself a "natural loner" though he was wise, productive & cared deeply for others. Introverts are brain-wired to prefer a low-stimulus environment. A person who lacks social skills or has or acquire mental illness may withdraw from others. The riddle is telling who is who.