In Harper Lee's "To Kill a Mockingbird," Jem Finch ages from ten to thirteen, becomes braver and able to stand up for what he believes in and learns how to cope with situations he cannot control. His left arm is also shorter than his right arm,because he broke it.
Jem's ideas of bravery become more defined as he ages. When he is ten, brave means touching the side of Boo Radley's house. But watching Atticus face a mad dog, Mrs. Dubose battle addiction and Scout confront a mob at the jail teaches him that true bravery means standing up for what you believe in and refusing to cede ground. After Dill runs away, Jem tells him to tell his mother where he is, but when Dill doesn't, he tells Atticus. Jem never apologies, though his friends shun him for a while.
Upset with the jury's conviction of Tom Robinson for raping a white woman, Jem rails against the town's justice system, convinced that the jury failed. Atticus lets him rant, giving him the space he needs to come to terms with the jury's decision. He also asks Scout to never bring up the courtroom again, since he doesn't believe Tom got the justice he deserved. In many ways, he goes through the stages of grief before accepting that he cannot control everything. Throughout the novel, he protects Scout, such as when Bob Ewell attempts to kill them both. Bob breaks Jem's left arm during the attack, leaving it shorter than his right arm.