As an introvert with a fairly active social life, I disagree with the general premise. I took an "always say 'yes'" approach for awhile. I accepted pretty much

As an introvert with a fairly active social life, I disagree with the general premise. I took an "always say 'yes'" approach for awhile. I accepted pretty much every invite I received. Eventually I found myself going out all the time, weekdays and weekends. At least once a week I'd have to schedule two or three events in a single day. It was exhausting in two ways. The obvious was that it's a pain to schedule so many things, and the nature of social events means you'll meet more people which is a positive feedback loop for more events. The other was that my personal growth was being limited. I skipped exercise/sports. I was unable to finish, or sometimes even work on, my personal art/programming projects. I realized it was a problem, and I no longer feel bad turning down event invites. Whether I am overbooked on events or if I just want to build a clay sculpture, I don't consider it to be selfish. Of course I still like to see my friends, and I still meet new people, but it's definitely not the only part of being a human.