You are foolish to say so.

你这样说是愚蠢的。

youdao

You are foolish to do it.

做这种事是愚蠢的。

youdao

You are foolish to throw away such a good chance.

你真蠢，丢掉这样一个好机会。

youdao

You say, well, why are you doing something so foolish?

你会说，你为什么在做那么傻的事啊？

麻省理工公开课 - 固态化学导论课程节选

When it comes to communicating well to audiences and the media, there is nothing foolish about consistency, as long as you are consistently conversational and fluid.

FORBES: Consistency Isn't So Foolish -Media Training

Or you want to rant about how barbaric and foolish gun owners are and how the Second Amendment was written in a totally different period in history.

CNN: On gun control, two places to start

Their pitch is simple: You are sitting on a pot-of-gold you would be foolish not to unload.

FORBES: It's Your Baby-- Now Say Goodbye