why does francis fail to miserably while hunting the lion

He fails on the original hunt of the lion because he panics when the lion charges him. Because of this "cowardice," his wife makes fun of him and hurts his feelings. The reader also feels that Wilson, the guide, may be the wife's lover. Later, Macomber is charged by a buffalo. He stands his ground, but his bullets go astray because he fires too high. Wilson then is charged and Macomber kills the buffalo at the last second. In the meantime, Margot (the wife) shoots from the car and her bullet hit Macomber and kills him.

Francis failed because after shooting the lion, he panicked and ran away when it came time to go in and finish it off. Thus, his lost face in front of his wife, as well as losing confidence in himself. Margot (his wife) saw his running away as a sign of cowardice..... note, she is already the authoritative figure in the home..... she emasculates her husband regularly, and her demands keep him subservient. What she sees as cowardice only serves to drive her into another man's bed. Francis loses on every front.