“Double down” comes from blackjack: when you’re confident, you double your...

https://fair-wiki.win/index.php/Uncertainty_Idioms_in_English_Explained

“Double down” comes from blackjack: when you’re confident, you double your original bet for a single extra card. Learners often misuse it to mean ‘try harder’ in any context—nope! It’s about risk and commitment, not just effort