Paul taught me this sentence yesterday: "You can't have your cake and eat it too". It's easy to understand. You have a cake and you have it. However, when you're eating it, you still have it for a while. After you finish it, it's gone. For example:
Paul: Haha!
Jason: Come on, I just wanted to ask a serious question, not a joke.
Paul: You can't have your cake and eat it too.
When you get marry, you can use this sentence to describe the freedom.