there's no such thing as a free lunch
said to emphasize that you cannot get something for nothing
天下没有免费的午餐
A: I get to travel with my job but the downside is I have to give talks.
我这份工作可以经常去四处走走，不过坏处是我得经常作报告。
B: Well, there's no such thing as a free lunch.
哎呀，天下没有免费的午餐嘛。
A: This advertisement says I can get an expensive camera for free!
这个广告说我可以免费得到一台昂贵的相机!
B: Don't be so gullible. There's no such thing as a free lunch.
别那么容易上当。天下没有免费的午餐。
