Bartleby starts off as an exemplary worker. As the narrator, his boss, explains:
At first Bartleby did an extraordinary quantity of writing. As if long famishing for something to copy, he seemed to gorge himself on my documents. There was no pause for digestion. He ran a day and night line, copying by sun-light and by candle-light.
Then, suddenly, Bartleby decides he "prefers not to" do his work. At first, it seems he burned himself out temporarily with overwork, but as it happens, his condition of "prefer[ring] not to" work becomes permanent.
On the first two occasions when Bartleby states his preference not to work, there is something in his quiet demeanor that is so odd that the narrator doesn't push him, though he says he would ordinarily have been very upset. The first time, too, the narrator is in a hurry, so he lets the incident pass.
Although he never knows exactly why Bartleby stops working, the narrator finds out at the end that Bartleby once worked for the Dead Letter Office, a place where lost letters end up. The narrator speculates that there...
was something so depressing about the futility of missed communication that the work broke Bartleby's spirit, making all effort seem futile.