Why are they split up in to 5 factions?

In a futuristic, dystopian Chicago, society is organized into five factions. Each faction places value solely on a specific virtue, which its members work to cultivate throughout their lives. There is Abnegation, which values selflessness, Amity, which values peace, Erudite, which values knowledge, Candor, which values honesty, and Dauntless, which values bravery. Children are raised in their parents' faction, and once they turn sixteen, they have the option to choose for themselves which faction will be theirs for the rest of their lives, whether it's the one they grew up in or not.