fool's errand

If you must stay, if you must go on your fools errand, at least take one or more of the men with you.

That I can promise you, and if I agreed to this proposition of yours I would be on a fools errand as well as you.

Pardon me if I say to you that I didnt come here on a fools errand.

A fools errand—but one that I must need go—and for that matter I myself am a fool.

To go in among the hidden gray shadows of the deep things is a fools errand.