“Double down” comes straight from blackjack: you double your bet when feeling...

https://dlf-ne.org/is-up-the-ante-a-gambling-term-unpacking-a-classic-business-idiom/

“Double down” comes straight from blackjack: you double your bet when feeling confident, risking more for a bigger win. Learners often confuse it with ‘double up,’ thinking it means ‘to increase’ anywhere. Nope