In the movie 21 how did counting cards help ben in the movie win blackjack?

Read the book Bringing Down The House and it will shed some light. Here is a basic lesson on how it works counting cards. If you see a 2-6 dealt to any player, dealer and you, then add 1 point each time a card of this cards come up. If you see a 10 through Ace come up, then deduct one point for each 10 through Ace. A deck with a positive count has more 10 through Ace vs. 2 through 6. This gives the player an edge because a 10 through Ace is more likely to come up vs. a 2 though 6 because there are fewer 2 through 6 cards in the deck. When the deck is positive, card counters wager more. When the deck is negative, they usually bet the table minimum. A negative count deck favors the house. The key to winning at card counting is to bet big when the deck is positive and win those hands. Not all hands will be won when the deck is positive just as not all hands are lost when the deck is negative. Having an edge or lacking an edge does not guarantee anyone a win, lose or push outcome. This includes the dealer's hand too. In the movie 21, Ben worked as part of a card counting team. Ben only played when the deck was hot with a positive count. His fellow teammates signaled him to enter the game by keeping track of the count and communicating it to him. If Ben were to play on his own then he'd have to play through hot decks and cold decks just like all card counters who work alone. I practice on my own time counting cards and I've played thousands of hands of 21. I can tell you this from my own experience. Roughly 1 deck in 15 turns out to be a red hot deck with a high positive count. The same goes for ice cold decks. About 1 in 15 goes ice cold with a big negative count. The remainder of the decks can be somewhat hot or cold. In my practice games I've won money on cold decks and lost money on hot decks. As I said a given count does not guarantee a win, lose or push for anyone including the dealer.