People used to be more content to spend time alone (as in by themselves), and this was healthy. Now, with all their activities, people tend to spend less time alone, but they feel lonelier.
 
Maybe Feeling alone when there are other people around has, in part, been enabled by technology. Technology has made it possible for us to conduct our business without actual face to face encounters: getting gas, checking out at stores and at the library, paying a toll, online shopping, online classes, face-book, email,etc… Maybe this kind of “trains” us not to interact with others as much as people once had to, so we aren’t in the habit of reaching out to others in person, and it carries over into our more personal lives.