“Double down” comes straight from blackjack: when you’re confident, you double...

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

“Double down” comes straight from blackjack: when you’re confident, you double your bet and hope for a lucky card. Learners often misuse it as just “doubling effort,” but it’s about risk—betting more when the stakes look good, not simply trying harder.