“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, hoping the next one seals the win. Learners often misuse it to mean just ‘try harder,’ missing the risk that doubling down actually involves