said to emphasize that you cannot get something for nothing

天下沒有免費的午餐

A: I get to travel with my job but the downside is I have to give talks.

我這份工作可以經(jīng)常去四處走走，不過壞處是我得經(jīng)常作報告。

B: Well, there's no such thing as a free lunch.

哎呀，天下沒有免費的午餐嘛。

A: This advertisement says I can get an expensive camera for free!

這個廣告說我可以免費得到一臺昂貴的相機!

B: Don't be so gullible. There's no such thing as a free lunch.

別那么容易上當。天下沒有免費的午餐。