There is no such thing as a free lunch.

天下没有免费的午餐。

Yet she is right about one thing: there is no such thing as a free lunch.

天下没有免费的午餐（there is no such thing as a free lunch）。

Yet she is right about one thing: there is no such thing as a free lunch. Something may appear to be free of charge, but there may be a hidden cost.

不过她在一件事上是对的，天下没有免费的午餐(there is no such thing as a free lunch)。有的东西看起来似乎是免费的，其实包含着隐藏费用。