“Double down” comes from blackjack—a bold move where you double your bet after...

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

“Double down” comes from blackjack—a bold move where you double your bet after seeing your first cards, betting on a strong hand. Learners often mistake it for just trying harder, but it’s really about raising the stakes, not just effort