Fail & Flail

Fail simply means to fail, that is be unsuccessful.
Flail, on the other hand, means to beat or to strike with or as if with a flail; that is, a manual threshing device consisting of a long wooden handle and a shorter, free swinging stick attached to its end: “In olden times, it was the norm to flail prisoners of war with ropes, sticks or anything you could lay your hands on.”