You hold a hard 10 (no ace counted as 11). The dealer shows a 8. Here is the mathematically correct basic-strategy play — and why.
| Double ← | +0.2866 |
| Hit | +0.1979 |
| Stand | -0.5105 |
| You bust on the next card | 0.0% |
| Dealer 8 busts | 24.5% |
Double is worth 0.0887 more per unit than Hit. On a $10 bet that is $0.89 handed over every time you get it wrong. Across the 340 situations in this chart it ranks 83rd by expected value — better than 257 of them, worse than 82. 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.
Hard 10 is a premium doubling hand. One card is very likely to give you a strong total, and against a 8 (which busts 24% of the time) you want maximum money on the table while you have the edge. Doubling wins you more in exactly the spots where you're a favourite.
If doubling isn't allowed (e.g. after hitting), simply hit instead — the extra card logic stays the same, you just can't add the extra bet.