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

https://milasultimatejournal.theglensecret.com/hedge-your-bets-finance-idiom-vs-everyday-use

“Double down” comes from blackjack, where you double your bet after seeing your first two cards, aiming for a bigger win but risking more. Learners often think it just means “try harder,” but it actually implies staking more on a risky move