“Double down” comes from blackjack, where you double your bet after seeing your...

https://averyscoolthoughtss.tearosediner.net/informal-english-idioms-for-business-meetings-what-you-didn-t-know-you-were-saying

“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.