When the dealer's upcard is an Ace, the table offers Insurance, a side bet costing 50% of your main wager and paying 2:1 if the hole card is a 10-value card. Holding a natural blackjack in that spot? The same proposition arrives under a friendlier name: Even Money, an instant 1:1 payout.
Mathematically, Even Money is identical to insuring a blackjack. A standard 52-card deck holds 10-value cards at a 30.7% ratio, which is not enough to justify a 2:1 payout, so buying insurance hands the house an average edge near 5.88%. Decline Even Money and the dealer has blackjack? Your hand pushes. If the dealer does not, you collect the full 3:2. Basic strategy therefore says never take Insurance or Even Money, unless you are genuinely tracking shoe composition through advanced card counting.
Two related situations are worth knowing. Non-insurable dealer blackjack: when the dealer shows a 10-value upcard, the hole card is checked automatically before anyone acts, and all bets except player blackjacks (which push) are collected. Dead hand: if every player busts before the dealer acts, the dealer does not complete their hand at all.