You're dealt a pair of 10s. The dealer shows a 4. Split or play it as one hand? Basic strategy answers:
| Stand ← | +0.6611 |
| Split | +0.4609 |
| Hit | -0.8547 |
| Double | -1.7094 |
| You bust on the next card | 92.3% |
| Dealer 4 busts | 39.4% |
Stand is not close: it beats Split by 0.2001 per unit. Getting this one wrong costs $2.00 on a $10 bet, every single time. Across the 340 situations in this chart it ranks 19th by expected value — better than 321 of them, worse than 18. 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.
Two ten-value cards make 20 — the second-best hand possible. Splitting trades one near-certain winner for two uncertain hands. Against a 4, keeping the 20 wins about twice as often as each split hand would. Never split 10s. Yes, even when the dealer shows a 6.