“Double down” comes from blackjack: you double your bet after the first two...

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

“Double down” comes from blackjack: you double your bet after the first two cards, confident you’ll win big. Learners often misuse it to simply “try harder,” missing the high-risk, high-reward nuance