“Double down” hails from blackjack—doubling your bet after seeing your cards,...

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

“Double down” hails from blackjack—doubling your bet after seeing your cards, betting on a better hand. Learners often misuse it to mean simply “try harder,” missing the risk-and-reward edge