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

https://shed-wiki.win/index.php/Transparent_and_Honest:_The_Idiom_%22Above_Board%22

“Double down” comes straight from blackjack, where you double your bet after seeing your first two cards, confident you’ll win big. Learners often misuse it to mean doubling effort generally—nope, it’s about risk, not just trying harder