“Double down” comes from blackjack, where you double your bet after seeing your...

https://www.pfdbookmark.win/double-down-hails-from-blackjack-when-you-double-your-original-bet-after

“Double down” comes from blackjack, where you double your bet after seeing your first two cards, aiming for a big win on one more. Learners often mess it up by thinking it means “back off” or play safe—it’s the opposite: you’re going all in