The simplest roulette, from 1 to 36, you can bet on odd number or even number, and you can get twice the money if you win. At this time, your winning rate as a gambler and a casino’s winning rate is 50% each. You and the casino are in a situation that both don’t make profit after long term. But casino had costs of hiring staff and doing business. If the winning rate is the same as you, the casino will have to close business.