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

https://troysbrilliantjournal.trexgame.net/up-the-ante-or-up-the-anti-which-is-correct

“Double down” comes from blackjack: you double your bet after seeing your first two cards, betting on a strong hand. Learners often misuse it to mean 'try harder' broadly, but it’s really about risking more when the odds look good