You hold a hard 9 (no ace counted as 11). The dealer shows a Ace. Here is the mathematically correct basic-strategy play — and why.
| Hit ← | -0.0657 |
| Double | -0.4329 |
| Stand | -0.6670 |
| You bust on the next card | 0.0% |
| Dealer Ace busts | 16.7% |
Hit is not close: it beats Double by 0.3672 per unit. Getting this one wrong costs $3.67 on a $10 bet, every single time. Across the 340 situations in this chart it ranks 200th by expected value — better than 140 of them, worse than 199. Expected value is per unit staked, computed for multi-deck, dealer stands on soft 17, double after split allowed. The model and the code are published as data.
A dealer Ace only busts about 12% of the time — most of the time they'll finish with 17 or better. Standing on hard 9 just waits to be beaten. Even though hitting busts you 0% of the time, improving your hand is the lesser risk against a strong dealer card.
Think of it this way: your 9 almost never wins as-is against a made dealer hand. The hit isn't reckless — it's the only path to a total that can actually win.