Plot hole: If Bradley Cooper was able to "quintuple" his money every day in the market as he claims to have done, he would have been able to earn the $100k he borrowed from a loan shark within a few days, starting from $800. Alternatively, he is shown in one scene winning a pot in poker where he could presumably also make a large amount of "seed" money from gambling. There was no need to borrow such a small sum of money from a loan shark, making the entire sub-plot unnecessary.
Character mistake: In the Italian restaurant, Eddie is speaking jibberish, not Italian at all.
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Suggested correction: He is speaking Italian.
I am Italian. He is speaking gibberish.
Suggested correction: The main character says he did quintuple his money four days in a row, not that he could continue to do so. "Presumably" he could do anything, like robbing a bank. Gambling is not a secure source of income, even with knowledge of the odds and every tell, he could also lose a lot of money.
He takes the seed money and then goes on to make a couple million with it on the stock market. There's really no reason he couldn't have just done that with the $800 seed money (also what the hell happened to that $10-20k stack of cash he took from Vernon's apartment? Somehow that was dwindled down to only $800?). The time constraint was totally artificial. He didn't need to conquer the world in 2 months except for the needs of the plot.