I pride myself in playing by the card in Blackjack. If you do that, you give yourself the best chance to win. But one thing I do disagree with it on is doubling down on 11 vs. the dealer showing a 10. Normally I'll double down on 11 vs. everything, but if you boil it down and you assume the dealer has a 10 underneath, that'd give them 20. So doubling my bet against a 20 when in that situation only a 10, J, Q, or K give you the win (28.6%) and a 9 (7.1% chance of pulling) gives you a tie. So 35.7% chance is solid, but doubling the bet is risky.
Not only that, but you limit yourself with hit cards there. If you get a lowcard like an A, 2, 3, 4, or 5 (35.7% chance), then you're stuck on that number. You could pull a 5 and be stuck on 16 vs. a 20, 19, 18, or even 17 from the dealer (28.6% chance). So you're obviously going to hit it, but doubling in my opinion is too risky.
This exact situation played out in my first solo session of Monday Night Blackjack. And what happened was exactly what you DON'T want to happen.
And I realize there are a lot of Blackjack purists that may disagree with my take here, but at the end of the day, this doesn't affect anything. Doubling down is just gatekeeping my pockets whereas I'm still hitting the hand. This just gives the player a little extra mobility as far as what to do on the second decision.
Another factor that actually changes the odds is how the dealer reveals Blackjack. With a 10 facing up, if they have an Ace below and are not required to check beforehand, then the smarter move is actually to just hit regularly.
"Something that won't affect most U.S. players but perhaps worth a mention is that strategy changes if the dealer doesn't peek for blackjack. With Aces in play as possible dealer down cards, doubling down is riskier and basic strategy calls for us to just hit hard 11 vs. 10." Per Atlantic City Weekly
So make sure you know the full rules when you're playing! And if you want to see how it goes, check out Hank and myself each Monday Night during the NFL season at halftime of the Monday Night Football game for Monday Night Blackjack.