Why does gatsby tell nick about his life? Do you believe gatsby? Does nick?

Gatsby gives Nick an account of his past in Chapter Four, his story, however, is highly improbable. Though he claims to descend from a prominent Midwestern family, when Nick asks him which Midwestern city he comes from, Gatsby hesitates, then says "San Francisco." He rattles off an absurdly long list of accomplishments: he claims to have studied at Oxford and lived in all of the capitals of Europe; then he enlisted in the war effort, where he was rapidly promoted to major and decorated by every Allied government, including Montenegro. He pulls out a photograph of himself in Oxford cricket whites, as well as a medal awarded by the government of Montenegro, in order to corroborate his story.

Though Nick was first taken with Gatsby's seeming purity and optimism, Gatsby remains enigmatic and not entirely trustworthy. Gatsby's own account of his illustrious past seems comically exaggerated. His readiness to provide evidence to corroborate his story is itself suspect; an honest man, one imagines, would be insulted by Nick's skepticism.