The phrase "to double down" means to increase one's efforts, commitment or risk in a particular situation. It is often used when someone decides to put more resources into something they believe will be successful, despite any previous setbacks or challenges. The term comes from the game of blackjack where if a player has placed a bet and receives a good card, they can choose to place an additional bet in the same amount as their original wager, effectively doubling down on their chances of winning.