Card counting when playing blackjack is not like it is on TV. The typical screen reference involves the character sitting there with a few chips and a smile, the shot changes to show the passage of normally a short amount of time and then cuts back to the hero, innocently smiling as he peers round a mountain of chips. Other references imply that card counters learn, over the course of a game, the location of every card in the deck, and know with confidence their opponents hands.
Sadly, Henry Sugar existed only in the fertile mind of Roald Dahl and the vast majority of screen writers are woefully ignorant of anything beyond dramatic imperative. That ignorance, and the romantic notions that ensue, mean that the phenomenon of card counting in blackjack has made more money for the casinos than card counters could ever hope to win back The truth is rather more pedestrian, but effective nonetheless if employed correctly and rigorously.
All card counting in blackjack does is give the counter an edge, nothing more. It does not guarantee he'll win every hand, far from it. It merely shifts the balance away from the casino and toward the blackjack player. The margin of advantage is small, averaging about 1% so as you can see, lurid promises that you can make easy money through card counting conveniently overlook the time and effort required to play blackjack successfully. In many instances in online blackjack, card counting simply doesn't work because the virtual pack is shuffled between hands.
Card counters don't keep track of individual cards played. Cards are assigned values, and the cumulative total of those values otherwise known as the running count is tallied. In ways that vary according to the card counting system employed, the running count indicates if the deck currently favours the blackjack player, or the casino.