Learning a simple card counting system can be a winning blackjack strategy
During the 1960s Las Vegas casinos used dirty blackjack strategy tricks to rig games in favor of the dealer.
Non-random shuffle tracking is a potential way to win at blackjack without using a card counting system.
Blackjack rules variations like deck penetration, payout and number of decks used have a major effect on the house edge.
Using a card counting is not the only way to win at blackjack but it is by far the best way.