It was this night that he told me the strange story of his youth with Dan Cody — told it to me because “Jay Gatsby.” had broken up like glass against Tom’s hard malice, and the long secret extravaganza was played out.
In Chapter 8 of The Great Gatsby, Nick leaps out of bed before dawn and to run to tell Gatsby a warning pressing upon his mind--a warning about his yellow car and his need to flee. Chapter 7 saw many events including the hit-and-run slaying of Myrtle Wilson. While violently arguing with her husband in his garage, she suddenly ran out in the road waving her arms--seemingly she had seen Gatsby's yellow car coming, recognized it and run out to stop Gatsby for aid. She wouldn't have known that Daisy was driving the car. Myrtle was slain instantly on impact. Gatsby tried to get Daisy to stop but in her hysteria, she sped faster and faster down the road. Gatsby eventually pulled the emergency brake, stopping the car, and Daisy crumbled over into his lap.
When Nick comes upon Gatsby in the yard of Daisy's home, Gatsby confesses that he will say he was driving. The driver of a car that Daisy sped past after the hit-and-run identified the car as yellow. This event ended a horrible day in New York during which Tom had brutalized both Daisy and Gatsby and made Daisy confess that she did not love Gatsby as he loved her. These two events together--the one following hard upon the heels of the other--are the cause for Gatsby's willingness to talk to Nick in Chapter 8 and confide in him in ways that he hadn't done before. As Nick says in his narration: Gatsby "had broken up like glass against Tom’s hard malice."