Blackjack is a game of skill and learning to count cards can give a player the advantage over the house. Your probability of winning a hand is dependent upon the mix of the cards remaining to be dealt. If the deck contains high cards it favors the player. If the deck contains low cards it favors the dealer. When you count cards you are keeping track of the ratio of the high and low cards left in the deck. One of the most popular card counting methods is the Hi Lo system. Here is how it works.