In casinos and other types of games of chance, such as slot machines, players individually compete for a prize pool with a casino operator who is directly involved in the gaming process. Accordingly, the players’ loss is in the interests of the operator. The more players lose, the more the casino wins. The more players play, the more they lose to the casino.
Casinos always get a guaranteed profit due to a slight, mathematically calculated advantage over the players. In different games, the casinos realized their advantage in different ways. For example, in roulette, this is the "zero" section (in the USA, there is also a "double zero" on roulette tables). In craps, this is a strictly calculated amount of bets that players can make. By lowering stakes and winnings, casinos always stay in the black.
The law of large numbers is the mathematical basis on which casino and slot machine owners build their profits. The more we gamble, the more predictable is the casino’s profit. At the beginning of the gaming day, the casino can even be in the red due to random fluctuations. However, by the end of the day, week, or month, when players have played many thousands of games, the law of large numbers will move most of the players' money into the pocket of the casino. Usually, casinos earn even more than mathematics allows because many players are inexperienced and make annoying mistakes.