Life As We Knew It was created after Pfeffer watched Meteor (1979), noting that "it got [her] thinking about how the people who have the most to lose if the world comes to an end are kids," and wanted to see how her characters would cope with a situation that was out of their control.

When asked about the change in narrative, Pfeffer stated that in her planning processes, she "just could not envision a teenage boy keeping a diary.

[2] Alex Morales is a seventeen-year-old Puerto Rican boy living in New York City with his parents and younger sisters, Briana and Julie, with his older brother, Carlos, serving in the Marines.

Tensions rise in the Morales household as Briana and Julie grow frustrated with the lack of information and they fear they will never see their parents again.

Jimmy and his wife Lorraine leave the city with their children to move to Tulsa and offer to take Julie, but Alex refuses.

Alex receives a postcard from Carlos, saying he has been deployed to Texas, and, despite their reluctance, he and his friend Kevin begin engaging in “body shopping”; looting abandoned corpses and selling their belongings for food and supplies.

Feeling guilty for what he has done to feed his sisters and his growing distance from God, Alex approaches Father Mulrooney to confess his sins.

Mulrooney assures him that his desire to keep his family alive is righteous and advises him to thank God for what he has when there is so much suffering in the world and to do something to make his sisters happy.

In November, Harvey, Alex’s supplies dealer, tells him that he can arrange for him and Briana to leave the city, but he must trade Julie away to an anonymous man.

Alex refuses, and in desperation visits Robert Flynn, the father of a wealthy former schoolmate, and asks for help in getting his sisters to a safe place.

Flynn warns him that the city will only last as long as a full evacuation, and gives him three passes to an unspecified safe location, which Alex hides from his sisters until the day comes for them to leave.

[4] Alex Morales: A 17-year-old Puerto Rican boy who is forced to care for Briana and Julie after the impact and blames himself for his supposed inability to help them.

Isabella Morales (Mami): Alex, Briana, and Julie's mother, who works as a nurse and is presumed dead after the subways are flooded.

"[5] John Green of the New York Times said that it "transcend[s] [its] premises with terrifyingly well-imagined futures and superb characterization," and that "the story’s climax and resolution feel achingly right.