In writing this novel, Hemmingway chose to focus on characters who depicted what were known as the "lost generation." This phrase denotes the men and women who, having lived through the horrors of World War I, found their beliefs and values about life, morality and love profoundly challenged. The Lost Generation, stripped of the moral framework that had supported them for so long, found themselves living aimless lives that were based on debauchery and immorality. This is something that is definitely seen in the character of Jake. The main action he engages in is moving from bar to bar, drinking excessively and being cruel towards those around him.
Even though Jake is a character who is aware of the emptiness of the Lost Generation, he does nothing to try and escape the rut that he is in. He acknowledges the pain of his situation and of his unrequited relationship with Brett, and he identifies the casual cruelty in which both he and his friends engage, yet he is a character who is curiously entrapped within the identity of being a member of the Lost Generation. Note how this is expressed in the following words Jake utters to Cohn in Chapter II:
You can't get away from yourself by moving from one place to another.
In response to Cohn's suggestion that travel to a new location to fill the void he senses within him, Jake identifies that the real problem with Cohn and the Lost Generation isn't location, it is a psychological problem that will be carried with them wherever they go. Interestingly therefore, Jake is very much a static character. He never attempts to move away from his realisation of the problems of being a member of the Lost Generation and is just as aimless and immoral at the end of the story as he is at the beginning.