“Double down” comes straight from blackjack. When you double down, you double...

https://stephensnicejournal.almoheet-travel.com/how-native-speakers-react-to-memorized-idioms

“Double down” comes straight from blackjack. When you double down, you double your bet after seeing your first two cards, hoping for a better hand. Learners often misuse it to mean ‘try harder’ in general—no, it’s riskier than that