I agree with this. From my experience, people who feel lonely (and feel saddened by that) tend to become overly worried about what others think of them and obsessed on making an impression. That usually leads to them becoming an echo chamber of themselves and starting to act "artificially", which is noticed by others as not being authentic. I'd say that sharing, which arises from mutual interest, is the cornerstone. So being in places where people authentically share mutual interests and cooperate is a great place to make friends. Sports associations (team sports, climbing, hiking, with the added bonus of physical activity being awesome for mental health) community centers with activities (chess, musical groups, dancing)...