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

https://www.slideserve.com/katherine_turner08/free-spins-and-scatter-symbols-explained-gambling-origins-meet-everyday-english

“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