Answer and Explanation:
"The Great Gatsby" is a novel by author F. Scott Fitzgerald, narrated from a first-person perspective by Nick. Nick is caught between the lies and affairs of the rich people who surround him: his cousin Daisy, her husband Tom, and her lover Gatsby.
Gatsby is the protagonist of the story: A mysterious millionaire who throws grand parties to whoever feels like showing up and whose business is unknown. People quickly begin to make malicious assumptions about Gatsby's past, including crimes such as murder.
In Chapter 4 of the book, Gatsby tells his version of his history to Nick. But he is only partially truthful. For instance, he claims to have attended Oxford, and even has a real picture to prove it. Truth is, he did attend Oxford for only five months as it was an opportunity given to some army officials. Gatsby takes half-truths and embellishes them to make his life more impressive. He's ashamed to have grown up poor.
Gatsby's true story - his poor childhood, his decision to become rich at whatever cost, his love for Daisy - is only revealed by him to Nick in Chapter 8, after an accident involving Gatsby and Daisy kills Tom's lover. However, Nick has already told readers the story in Chapter 6. The reason why he chose to tell the story before the chronological moment when it was indeed told is as follows:
"He told me all this very much later, but I've put it down here with the idea of exploding those first wild rumors about his antecedents, which weren't even faintly true."
Nick cares about Gatsby so much that he chooses to tell his true story earlier in the book so that readers won't misjudge Gatsby.