John Grochowski Some blackjack players never learn basic strategy. Some memorize the chart but can't quite convince themselves that all the plays are in their best interest. Whatever the cause, some mistakes crop up over and over. Let's look at a few I see frequently. They're not necessarily the costliest mistakes possible, but players don't make errors such as hitting 20. These are mistakes players make all too often. ACE-7 vs. 9: Players stand on soft 18 a LOT more often than on soft 17. It's better to double down if the dealer has anything from 2 through 6 up, but standing is the basic strategy play if the dealer shows 7 or 8.