I assume you haven't heard of "card counting", which is a famous way to beat the house advantage in blackjack. Of course, if they suspect you're doing it, they'll kick you out.
I was under the impression that casino's operated with either continuous shuffling, or enough packs of cards to effectively negate the benefits of card counting these days
Also many casinos offer special blackjack promotions that mean you don't even need to count cards to win.