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

https://xeon-wiki.win/index.php/Idioms_That_Sound_Negative_but_Are_Actually_Neutral

“Double down” comes from blackjack, where you double your bet after seeing your first two cards, risking more to win big. Learners often confuse it with just trying harder—nope, it’s about upping the stakes, not effort