Why should I double against a (possible) pat hand?
The parentheses in the question are oursbecause at the point where the decision to double is made, you’ve only seen the upcard, so you don’t really know whether the dealer has a pat hand. You’re assuming the dealer has a ten in the hole; there’s a strategy based on the ten-in-the-hole assumption, and it’s quite a bad one.
Basic strategy considers every likely value of every unknown card, so even if the dealer’s showing a seven or higher, that doesn’t guarantee a pat hand. It’s a possibility, but not a probability: though there’s a 38.4% chance the dealer’s got a ten or an ace in the hole to complete a pat hand, there’s a 62.6% chance he doesn’t. On top of that, you’re just as likely to draw a high value card to your hand to match or beat the dealer’s total.
Reluctance to double against a scare card falls into the same category as reluctance to hit a fifteen. You’re in a tense situation and you’re looking for an easy way outbut you’re being scared of the wrong thing. If you can’t leather up and follow basic strategy in difficult situations, you’re playing by yourgut, and will most likely get fleeced.