The impotence that Jake suffers from acts as a very powerful metaphor for the way that war had changed perceptions of masculinity and challenged what it was to be a man. Whereas before, war was a matter of personal valour and bravery in the face of the enemy, the reality of trench warfare in World War I where thousands died without even facing their enemy thanks to gas attacks and bombs profoundly challenged what it was to be a man, as survival seemed to be based more on luck than on any other objective characteristic, such as skill. Jake, significantly, is rendered impotent thanks to an injury sustained during the war, and this therefore represents the challenge to masculinity that World War I represented. However, at the same time, it also acts as a kind of symbol of the so-called "lost generation," or the aimlessness of the young men and women who, having experienced war, found themselves unable to engage with life and wandered around aimlessly, without purpose or goal. This aimlessness is expressed in a variety of ways in the novel, but most importantly perhaps through the constant drunken carousing and debauchery of the characters. Jake himself picks up on this aimlessness when he says to Cohn, after Cohn expresses a desire to move to Spain from Paris, that the real issue isn't his current location but an internal problem:
You can’t get away from yourself by moving from one place to another.
Jake inherently recognises that the problem with the lost generation is something internal rather than external, just as his impotence is external and external. Jake, just like the other main characters, shows that he is unable to commit to a meaningful relationship and be productive in society, and his impotence acts therefore as a metaphor that characterises the failings of the main characters: all are impotent, in their own different ways.