One of the biggest gambling myths is that when an event doesn't occur for a long time, it becomes overdue and is more likely to happen. This is often referred to as "the gambler's fallacy". There are lots of gambling systems out there that exploit this myth, all equally useless. In games of pure chance the probability of an event current has the same probability each time the game is played. This is especially true in games like lotteries, keno and roulette.
There are basically three types of betting or gambling systems - positive progression betting systems, negative progression betting systems and insurance betting systems. Positive progression systems increase the bet when there is a win. This is similar to let it ride and requires less money and is often used during a winning streak. Negative progression systems increase the bet when there is a loss. These require lots of money, large table limits and are often used to recover from a loss. This can be dangerous and when you lose you lose big. Insurance bets decrease the amount of your bet when you win usually after a large first bet or a short series of let it ride wins.
One of the most common gambling systems is the Martingale. This is a negative progression system that involves doubling a bet after a loss and is usually applied to even money games like red/black in roulette or pass/don't pass in craps. The theory is that by doubling after a loss you will eventually win back all your money plus a little extra. The problem with this theory is that it requires very high betting limits and a huge bank roll. This system has been tested in a computer simulation and was shown to have no improvement over flat betting of the same bet for every hand.
All gambling systems are based on the assumption that if you've lost one, two or ten times in a row, your chances of winning are better now than when you started.
The only time a betting system is useful is when its applied in conjunction with another system like card counting. Betting systems are really only useful if you have some idea about the outcome of the game. Card counting in a game like blackjack gives you some idea about the cards to be played. A betting system allows you to adjust your bets based on the results of your card calculations.
Unfortunately, the bad news is that none of these or other systems will help you win at the casinos. Games of chance are just that, or they wouldn't call it gambling. If you are interested in reducing the house advantage, they you should seek out games in which skill has as much to do with it as luck, like blackjack or poker.
Some people believe that if you use a system at a casino you will be banned from the casino. The fact is, all casinos love system players. Casinos know that systems will not gain players any real advantage over the casino. The casino know that these players will keep coming back to try their system, so they welcome their business. The only system players that the casino doesn't like very much are blackjack card counters. They can get a real advantage on the casino and those players will be asked to leave if they catch on.