“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, betting bigger on a strong hand. Many learners misuse it to mean ‘try twice’—it’s really about committing more when you’re confident, not repeating an action.