英語のことわざ

You cannot have your cake and eat it

If you eat a cake, you can't keep (have) it for later. If you keep a cake for later, you can't eat it now. This proverb means that you have to make a choice between two incompatible options. You can't choose both options. It is used particularly when someone wants to enjoy something without making the necessary sacrifices. For example, you can't continue eating 10 donuts a day and expect to get fit.