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The problem with betting revolves around the very nature on where it is founded- which is luck. There are times that some can potentially cash-out large sums of money and others lose significant amounts in one night. It all depends if the person knows when to stop his gambling especially if he/she is on a losing streak.
If someone wins large sums, this does not always mean luck. Maybe it's laundering dirty money) And ordinary players play either to a big win, or to a complete loss.