In Lord Jim, the book's namesake makes one whopper of a bad choice. It's a choice he just can't seem to bounce back from and he spends the rest of the novel trying to understand it, justify it, escape it, and rise above it. In one weak, fleeting moment aboard the Patna, Jim makes a snap decision that throws a big ol' wrench into the rest of his life. The aftermath takes us through the rest of the novel, and reminds us that while choices can be made in a matter of seconds, their consequences can last a lifetime.
While onboard the Patna, Jim jumps ship based on pure instinct. He has no choice in the matter. But for the rest of the novel he's making the choice to be continually ashamed of his actions.
Jim chooses to go to his death at the hands of Doramin at the end of the novel as a way to make up for his choice to jump ship aboard the Patna.