Counting cards is an in-depth method that is difficult to cover on a single page, but when you learn how to count cards in blackjack, you can gain an edge against the casino. Because blackjacks pay more than even money and you have the opportunity to double and split in favorable situations, if you can change the bet size based on the remaining cards in the single or multiple decks you can shift the house edge to your advantage when you play blackjack and other casino card games.