Part of the current huge popularity of Blackjack comes not just from its simple rules but from the fact that it is one of the few traditional casino games in which smart players can gain an edge in the odds over the house. They do so in real-world casinos by a technique known as “card counting,” in which they observe and mentally record all cards dealt as a game proceeds. With that knowledge, a mentally adept player, particularly one who has studied statistical computer analyses of the game and various scenarios, knows with ever-greater certainty the likelihood of certain cards being dealt from those remaining in the deck with each passing hand, thus increasing or decreasing bets depending on what cards are dealt in each particular hand.

Real-world casinos watch for signs of card-counting and ban its practitioners. Online casinos eliminate it as a possibility by continuous shuffling.