"Double down" comes from blackjack: you double your bet when you’re confident...
https://www.bookmark-suggest.win/double-down-comes-from-blackjack-where-you-double-your-bet-after-seeing-your-1
"Double down" comes from blackjack: you double your bet when you’re confident your next card will win. Many learners think it means 'try harder,' but it’s more specific—commit more to a risky move. Use it when you’re doubling your stake, not just effort.