“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—bold move, high stakes. Learners often misuse it to mean just ‘try harder,’ but it’s really about risking more because you’re confident