There are some so-called blackjack strategies out there that players no in the know will swear by. Assuming that the dealer has a card worth 10 for a hole card is one such strategy.
Sure on the surface it might sound like an okay strategy to use in blackjack, almost like it is a safety net based on the player assuming the worse. But the statistics do not add up on this one. And it is those statistics that show it as the bad blackjack strategy that it is.
To begin with, and to make the math simple at first, we are going to look at a single deck. In a single suit there are thirteen cards. All of those cards have their face value applied in blackjack except for the three face cards and the Ace which has the ability to be played as a 1 or an 11; the three face cards (Jack, Queen and King) are each worth 10. So out of thirteen cards in a single suit, only four (10, Jack, Queen and King) are worth 10; obviously the other nine cards are not worth 10.