Sonder
n. the realization that each random passerby is living a life as vivid and complex as your own—populated with their own ambitions, friends, routines, worries and inherited craziness—an epic story that continues invisibly around you like an anthill sprawling deep underground, with elaborate passageways to thousands of other lives that you’ll never know existed, in which you might appear only once, as an extra sipping coffee in the background, as a blur of traffic passing on the highway, as a lighted window at dusk. (From the dictionaryofobscuresorrows.com)
A select many characters in The Bluest Eye are given in-depth backgrounds worthy of a protagonist of a usual novel. Some, like Cholly, are introduced as near-one dimensional character as merely the one who burned the Breedlove's house down. To the reader, Cholly is just the person who committed arson and was sentenced to jail...among other things. But we aren't to see him like that. His story is fully fleshed out with his childhood life with Aunt Jimmy and onwards to his marriage with Pauline. Like Cholly, Pauline is another character who has a life and has the right to be the protagonist of her own life.
These are but two examples and though The Bluest Eye doesn't explore the lives of every single character, it is a substantial amount as compared to many, many other novels. The relation of bringing sonder as an element helps permit the novel to reflect reality. Everyone has a story. This portrayal is extremely important in actually showing someone the world apart from what they see for themselves, from the usual standpoint of "the protagonist." Perhaps there are too many with this sort of thinking and need a wake up call.