"Being lonely isn’t the same as being alone. Cacioppo is careful to clarify this distinction in every public lecture and conference talk he gives (and there are many, usually pretty crowded). Lonely people, he’s found, are as likely as anyone to be surrounded by coworkers, neighbors, friends, and family. They’re no less attractive or intelligent or popular. What sets the lonely apart is a perceived isolation, the sense that their relationships do not meet their social needs."
