an ace up one's sleeve

Image acquired from Wikimedia Commons and used with permission. Left image attribution: public domain. Right image attribution: Christian Glaeser

Explanation:

Some people always win when they play cards. Some people win some of the time, and some people always lose. Those who lose at cards have found a way to solve this problem; they cheat. Since an "ace" is the most powerful card in most card games, it's a good idea to have one when it is needed. A tricky player can do this by keeping an ace hidden in the sleeve of his shirt. That way, when he starts losing, he has an ace up his sleeve which can give him a secret advantage.

An ace up one's sleeve is a hidden yet powerful solution that a person can use to get an advantage in a situation.

Example:

Jack: Hey Bill. Guess what? We are going to have another five hour meeting today where the boss will tell us about all the things we're doing wrong.

Bill: No, not this time Jack.

Jack: What do you mean? These meetings are mandatory; we have to go.

Bill: Not necessarily. This time, I've got an ace up my sleeve. You see, I paid some guy on the street to come in here and run around like a crazy chicken just before the meeting starts. While everyone in the building is chasing him, we just quietly walk away.

Jack: That's brilliant Bill! You're the one who should be boss!

Bill: Someday Jack. Someday.

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