"Double down" comes from blackjack—when you double your bet after seeing your...

https://www.bookmarkingtraffic.win/double-down-means-to-commit-fully-to-a-risky-choice-from-blackjack-where-you

"Double down" comes from blackjack—when you double your bet after seeing your first two cards, betting you’re onto a winner. Language learners often overuse it, thinking it means just 'try harder.' Nope, it’s about risk, not effort