If you could only take one card, doubling would be higher EV. the reason you hit is the odds of getting a low card (ace,2,3,4) where you’d want to hit again on a soft 13 is high enough and the odds of a dealer bust are low enough that optimal play isn’t to double.

So you're saying there are strategies that give you a higher probability of winning black jack other than sensible guessing?

Lets assume Vegas BJ (6 deck H17 DAS), If I say exception, it would be beneficial to ignore the exceptions until you are completely solid with the fundamental logic and can add the exceptions.

If your hand is a hard hand (5-20):

An important fundamental is to know when the dealer has a weak upcard. A dealer showing 2-6 has a weak upcard, while a dealer showing 7-A has a strong upcard. Why? If we assume the dealer has a hidden ten, then the strong dealer with 7-A will likely pat their hand, and the weak dealer with 2-6 will have 12-16, and easily bust.

Since we go first, we want to stand before we have the chance to bust against a weak dealer upcard, so the dealer busts instead. With a strong dealer upcard, we want to take the risk of either tie or beating the dealer's probable pat hand, at the risk of busting out early.

First, determine if you should double, if your hand is 12 or more, never double. If you see 11 or less, take a moment to figure out if you should double or not.

Rules for hard hands 11 or below:

• If your hand is 11: double always, if we draw 10, we hit 21 and likely win

• If your hand is 10: double always except 10 and Ace, same logic as 11, but a push with 20 is not worth the extra risk of doubling

• If your hand is 9: double against weak upcards (2-6), logic is that taking a 10 results in 19, a decent hand, and a weak dealer upcard means they bust more often even if we don't make 19. (EXCEPTION: ignore until you are comfortable, you don't double 9 v dealer 2)

• If your hand is 8 or less: hit always, total is too low to double, and you can't bust.

Rules for hard hands above 12:

• If dealer has weak upcard (2-6), always stand. Logic is that we want dealer to bust rather than take the chance to improve hand. (EXCEPTION: ignore until comfortable, you hit 12 v dealer 2 and 12 v dealer 3)

• If the dealer has a strong upcard (7-A), hit until 17 or more. The logic is that dealer is likely to make a pat hand, and we need to try and beat it, even if we have to risk busting out.

That's it for hard hands, now we have to go to soft hands. Soft hands are any hand with an Ace.

The logic with soft hands is that soft 19 is already good enough that we don't risk making it better. We want to add more money to the table when we can double at no risk and the dealer upcard is weak.

First thing is to determine if we double or not, here are the criteria to determine if we double or not

1. Your hand total has to be soft 18 (A,7) or less (EXCEPTION use only when comfortable: You double soft 19 vs dealer 6)

2. The dealer has to have a weak upcard (2-6)

3. If the dealer's upcard is 5 or 6, double, if not, proceed to step 4

4. The rule of 9: add the total of your non-ace card with the dealer's upcard, if they equal 9 or more, double (example: double A,5 v dealer 4 [equals 9], don't double A,3 v dealer 3 [equals 6]) (EXCEPTION: you double A,4 v dealer 4 even though they equal 8)

If you can't double:

• If dealer has weak upcard (2-6), hit until soft 18 or more, if hand becomes hard, follow hard rules. Logic is that 18 is a good enough hand to beat most weak dealer upcards. You may think 17 is good enough, but 17 will never win against a pat dealer hand (only tie). Any hand less than 17 only relies on dealer busting, and we want to take the chance to increase our odds of winning by making a hand greater than 17 because we can't bust with a soft hand. If we go over to a hard hand, its not a big deal, we are back where we started.

• if dealer has 7 or 8, hit until soft 18 or more, if hand becomes hard, follow hard rules. Logic is that soft 18 beats dealer 7 upcard and ties dealer 8 upcard.

• if dealer has 9 or higher, hit until soft 19 or more, if hand becomes hard, follow hard rules. Logic is that we are very unlikely to improve soft 19 (only 20 or 21 is better). Now you will get people yelling at you for hitting soft 18 vs 9, but soft 18 does not beat the probable dealer 19.

Now the splits. We offensively split (by put more money down) when the dealer is more likely to bust, we defensively split when the totals of the single cards improve our odds of beating the dealer (even at the cost of doubling your bet).

Always split:

• A,A : If you get 10s, you get 21 right away

• 8,8: 16 is the worst card to have in BJ (20% win chance), whereas two 8s, with the higher chance of hitting 18, is better (even if we risk more money).

Never split:

• 5,5 : You should be doubling 10s. Whereas splitting 5s, with the higher likelihood of getting two 15s (a horrible hand), is not smart

• 10,10: hard 20 is a great hand to have, why ruin it?

The rest, follow these steps:

1. Does the dealer have a weak upcard (2-6?) (if not, read below)

2. Is the upcard 5 or 6? Split

3. Is the upcard 2, 3, 4? Split (except 4,4). The logic about 4,4 is that hard 8 is a decent hard, where two hands of 14 isn't so great. (EXCEPTION only use once comfortable: split 2,2 and 3,3 against 7 upcard)

The weird splits: If the dealer upcard is strong, imagine splitting the hand and receiving a 10. If the result is a tie or win, then split.

• 7,7 : split against dealer 7, 17 ties probable dealer 17

• 9,9: split against dealer 8 or 9. 19 beats probable dealer 18. 19 ties probable dealer 19. Don't split against dealer 7, since hard 18 already beats probable dealer 17.

That's everything, good luck