Many casino games such as slots and any lottery-based games such as keno and bingo offer players fixed odds and as they are games of pure chance there is very little the casino player can do to manipulate them and improve them to their favor.
In Slots and Lottery games the odds do not change no matter how the player plays or whether they have some strategy they follow. Games of chance often create playing habits but those have more to do with the player's character than any mathematically base strategic thinking.
This is not the case with the game of blackjack where players can without a doubt improve their playing strategy and thus increasing their chances of playing the best possible blackjack with the cards they are dealt.
One of the key principles for improving your blackjack odds is to understand that a hand of blackjack is not an independent event that has no bearing on future hands. Rather that every removal of cards throughout the process of playing the game can increase or decrease the player's chance of a win. This makes the ability to retain in memory discarded cards is of great benefit.
The process of removal of used cards from the shoe of cards still in use generates a situation where the odds of receiving specific cards or some combination of cards changes and as such affects the odds both for the player and the casino, so in fact the odds in the game are ever-changing with every hand that is finished playing.
The odds become more favorable to the player when low cards such as 2 to 7 have been discarded. And there is a high ratio of 9's, 10's and Aces remaining in the deck still in play.
Most of the card counting systems work on the principle of keeping track of the ratio between high and low cards that remain in the game. When the game is just commencing and all cards are present its an even game between the casino and player and the game's balance is tipped to single-hand strategy and luck of the draw.
As the game progresses the dominant winning theory states that players need to bet more when their chances of winning are higher after many of the low cards have been discarded. And bet less when the situation is reversed.