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You don't have to be a professional mathematician to multiply EV by Amount Bet. But there is a thing called variance, usually expressed as standard deviation.

If you overbet your advantage, (or take bets that are larger than your advantage in relationship to your bankroll), you go broke.

Search the web for "Kelly Betting" and you should find an explanation of proper bankroll size and bet amounts based on variance.

There is more to bet sizing and bankroll than the question "Is it +EV or not".

And as pzhon refuses to admit, if you are overbetting your advantage, if you are underbankrolled you still stand a very good chance of going broke even making +EV bets.