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

https://xeon-wiki.win/index.php/Blue_Chip_Companies:_Meaning,_History,_and_Their_Gambling_Origins

“Double down” comes from blackjack, where you double your bet after seeing your first two cards, hoping to beat the dealer. Learners often use it to mean “try harder” generally, but it’s specifically about risk—doubling your stake, not just effort