In blackjack, an Ace can only count as 1, while a 2 can count as either a low or high. This means that if you have a 2 card, it’s best to put it on the dealer’s face-up card. Theoretically, this would give you a better chance of getting a blackjack, as the dealer would have to hit one of your two cards instead of simply drawing one. However, there are several factors that can affect whether or not this strategy will work in reality.
For one, if the dealer has a high card (a 9, 10, or A), then he may be able to stay in the game even if he hits your 2 card. Additionally, some casinos have rules that allow the dealer to split any two cards (including a 2) for even money. So even if you put your 2 on the dealer’s face-up card, you may not actually gain anything by doing so. So while putting a 2 on the dealer’s card is theoretically advantageous in blackjack, it won’t always be successful in practice.