“Double down” comes from blackjack: you double your bet after the first two...

https://dlf-ne.org/is-up-the-ante-a-gambling-term-unpacking-a-classic-business-idiom/

“Double down” comes from blackjack: you double your bet after the first two cards, confident you’ll win big. Learners often misuse it to simply “try harder,” missing the high-risk, high-reward nuance