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

https://idiominsider.com/talking-odds-at-work-the-risk-idioms-every-english-learner-gets-slightly-wrong/

“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