The mistakes that cost you the most
Basic strategy errors are not all equal. Some barely matter, and some bleed real money every time.
Short answer
The single costliest habit is playing stiff hands too passively against a weak dealer upcard, and standing on hard 16 vs 10 instead of surrendering when it is offered. Below are the per-unit expected-value costs this engine measures for a handful of the most common misplays in a six-deck game where the dealer stands on soft 17.
The most costly common mistakes
| Mistake | EV cost per unit |
|---|---|
| Hitting a hard 13 against a 6 instead of standing | 0.08 |
| Not doubling 11 against a dealer 10 | 0.06 |
| Not splitting 8s against a 10 | 0.05 |
| Standing on 12 against a 3 instead of hitting | 0.04 |
| Standing on 16 against a 10 instead of surrendering | 0.04 |
| Standing on soft 18 against a 10 instead of hitting | 0.04 |
These costs are per unit bet, per occurrence — play a few hundred hands and a habit like standing on a hard 13 against a 6 adds up to a meaningful chunk of your action. Play a few hundred hands in the trainer's drill modes and its accuracy heatmap will show which of these you get wrong, so you can fix the expensive habits first.
Two mistakes worth calling out
- Never taking insurance is not a mistake — taking it is. See side bets & insurance for why declining is correct without a card count.
- Splitting 10s. A made 20 is one of the strongest hands in the game; breaking it into two separate 10s to chase a split rarely improves on standing. It is never correct in the decision library's pairs chart.
Why decision-by-decision grading catches these
A strategy chart tells you the rule, but it cannot tell you which rules you keep breaking. The trainer grades every hit, stand, double, split, and surrender decision, names the exact rule you missed, and tracks your accuracy by hand category, so recurring leaks show up in your numbers instead of your bankroll.
Common questions
What is the single most valuable fix?
Stop hitting a hard 13 against a dealer 6. It is the largest single-mistake cost measured here, and it is one of the more common errors because a 13 feels fragile even though the dealer is the one at risk.
Is surrendering hard 16 vs 10 really worth it?
Yes. Every option on that hand loses money on average, and surrender loses the least — see the full breakdown on hard 16 vs 10.
How do I fix these habits?
Drill the specific hand types you get wrong in the trainer rather than playing full shoes at random. The adaptive drill feeds you more of whatever hand type you are currently weakest at.