ace up one's sleeve

The phrase "ace up one's sleeve" refers to having a secret or hidden advantage or resource that can be used to gain an advantage or achieve success, especially in a competitive or challenging situation. It originated from the practice of cheating in card games, where a player would conceal an ace (a high-ranking card) up their sleeve, and then discreetly introduce it into the game to gain an unfair advantage over their opponents. Thus, having an "ace up one's sleeve" metaphorically implies having a hidden advantage that can be strategically utilized when needed.