In 21, when you have two cards of the same number, you can split the hand into two hands and “double down” your bet. Let’s say you bet $10 and are dealt a pair of 8s. You can view this a single hand of 16 and choose to hit or stand, or you can split the hand into two new hands, getting a fresh second card for each. However, in so doing, you must pay an additional $10 wager of the new hand you’ve added. Knowing when to split in blackjack can be the difference between a big loss and life-changing win when the stakes are high.