I suppose the equation is different for someone who is perpetually single. That one person makes a big difference.

If you're single and you don't want to be, you kind of have to learn extroversion cargo-cult behavior (being a bit more outgoing, interesting and interested in conversation and people, make first moves socially, etc.). Then you hopefully find a partner that's a bit introverted and you get out of there! I speak entirely subjectively as someone who lived in a city a long time and found it dreadful as an introvert.