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

https://wiki-coast.win/index.php/How_Native_Speakers_React_to_Memorized_Idioms

“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