Revealing mistake: When Gatsby and Tom are racing (a CGI achieved scene), note that the passengers' hair barely moves. (01:32:00)
Revealing mistake: The doctor tells Nick to write his story and Nick says he isn't any good. The next shot shows a blue screen reflected in the doctor's glasses. (00:14:00)
Revealing mistake: When Nick starts talking about Gatsby to his doctor, a green reflection is visible in the doctor's glasses when the doctor says "Where'd you meet him?" There's no other object in the room that is that style of green (it's most likely a green screen). (00:03:00)
Chosen answer: This has been answered before. Gatsby grew up in a poor, mid-western family. He is a self-made millionaire (through illegal means) but pretends he comes from wealthy, upper-class society. He has adopted a fake posh accent to help support the illusion of his bogus background. It is how he believes well-bred people speak.
raywest ★