Obviously the first place my brain went was to a totalitarian post-apocalyptic society. Instead of The Giver or Divergent where you have to select your lifelong identity as a tender youth, in this one at 30 you have to cut 30% of the people you love out of your life. It's for population control, but only the lower classes have to do it (although maybe the reproduction of the rich is so tightly controlled they never really have to?)
Nobody quite knows what happens to the people you reject, except that you never see them again. Some say they go to an alternate society where all their needs are provided for. Some say they get put out on ice flows. Some say they are turned into food.
When a plucky, rebellious 28 year-old befriends a rich girl who happens to be the daughter of the "democratically elected" president, everything changes.
Possible plot hole: what happens if you reject someone, but someone else chooses them? Do you wind up in a society with only the friends you have chosen? Where is everyone else? Or do groups of friends band together and strategically pick their lists so that everyone can be included in someone's list?