The article continues beyond that sentence!
> But you can be alone and not feel lonely, or you can be with others and feel lonely. “Loneliness really refers to perceived social inadequacy of relationships
> “One of the clearest findings on solitude is if it’s chosen for the value that it has, it’s going to be a more positive experience,” says Netta Weinstein, a professor of psychology at the University of Reading in England and a co-author of “Solitude: The Science and Power of Being Alone.” “If it’s forced on you, it’s going to be a less positive experience.”