Matched is a 2010 young-adult dystopian novel by Aly Condie, about a future world where all marriages are decided by genetics and mathematical algorithms.
In the novel, the Society has strict control over marriage and equality, keeping its citizens separated by law and status; law-breakers are called Aberrations and prevented from marrying. Cassia, the protagonist, is somehow matched with Xander, a normal citizen, and Ky, an Aberration; she is societally bound to marry Xander but feels a deep connection with Ky as well.
The central conflict is between freedom of choice by the individual and the will of the Society who claims to know "what is best." Cassia believes in the Society until her double-match, and this flaw in the Society's good intentions allows her to develop individual thought. Instead of bringing her peace and security, the Society has brought her doubt and fear, especially since she develops a friendship with Ky and discovers that his Aberration status is entirely subjective, having no effect on his personality. He is just as normal as she is, but the Society has stamped his future out because of his father's crimes; Cassia knows that this is not the action of a benevolent government. Her individual choice opposing the Society's will provides her motivation and the conflict of the story.