I think rules of the specific variant being played like Different blackjack games have different rules, such as the number of decks used, whether the dealer hits or stands on a soft 17, the payout for a natural blackjack, and more. These rules can impact the odds of winning, and therefore affect the effectiveness of certain strategies.The number of decks being used like The more decks that are in play, the higher the house edge typically becomes. This is because it becomes more difficult to predict which cards will be dealt in future rounds.