Start with the baseline assumption that people are broadly similar to the people they're friends with -- i.e. socialites are friends with socialites, loners are friends with loners.
Overlay that with the observation that you're more likely to be friends with someone who has lots of friends, and less likely to be friends with someone who has few friends.
Consider the extremes: You're certain to be friends with someone who is friends with everyone, and certain to not be friends with someone who has no friends.
Start with the baseline assumption that people are broadly similar to the people they're friends with -- i.e. socialites are friends with socialites, loners are friends with loners.
Overlay that with the observation that you're more likely to be friends with someone who has lots of friends, and less likely to be friends with someone who has few friends.
Consider the extremes: You're certain to be friends with someone who is friends with everyone, and certain to not be friends with someone who has no friends.