“Double down” comes straight from blackjack: you double your bet when you’re...

https://www.active-bookmarks.win/double-down-comes-from-blackjack-where-you-double-your-bet-after-seeing-your

“Double down” comes straight from blackjack: you double your bet when you’re confident your hand will win. Language learners often misuse it thinking it means "do something twice," but it’s about increasing commitment, not repetition