“Double down” comes straight from blackjack—when a player doubles their bet...

https://idiominsider.com/talking-odds-at-work-the-risk-idioms-every-english-learner-gets-slightly-wrong/

“Double down” comes straight from blackjack—when a player doubles their bet after seeing the first two cards, hoping for a strong hand. Learners often misuse it to mean “just try harder” generally. Nope