Comments by "EebstertheGreat" (@EebstertheGreat) on "Looking at Shuffling (extra footage) - Numberphile" video.
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Vee The deck is not shuffled after every hand of blackjack. Doing so would cost a huge amount of time, massively cutting into house profits (and also frustrating the players). Instead, a blank card is inserted into the deck (or shoe), and the deck is shuffled when that card is reached. In order to reduce the advantage players can gain by counting cards, a shoe with 4 to 8 decks is typically used, and at least 25% of the cards remain below the cut. Even so, it is possible to gain an advantage by counting cards in some situations, though usually a very small one.
Moreover, shuffle tracking is at least allegedly used by expert gamblers in blackjack, not when these players are shuffling the cards themselves, but when they are watching the dealer shuffle them. Because large stacks are difficult to shuffle, clumps of cards often tend to stay relatively close together after a shuffle, allowing observant players to keep track of certain sequences and thus gain information about which cards are more probable to come up next. If people in casinos were allowed to shuffle the cards themselves, cheating would be absolutely rampant, and it is certainly possible for practiced hands to perform controlled shuffles. You don't need to be perfect to beat the small house edge.
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