Jem expected the verdict to be “not guilty,” but Atticus expected to lose.
When the trial ends, Jem seems very confident. Atticus tells him he does not know if he is going to win or lose. Scout describes Atticus as “exhausted.”
Jem was jumping in excitement. "We've won, haven't we?"
"I've no idea," said Atticus shortly. (ch 21)
Actually, Atticus does have a pretty good idea. He is confident he will lose, despite his best efforts. He knows that the jury would never acquit a black man accused of raping a white woman, even if there was no way he could have committed the crime. The racism was just too deep. Guilt as accused was the justice system for blacks in Maycomb.
Back in chapter 9, Scout asked Atticus if he was going to win the trial. Atticus gave a definitive answer.
"Simply because we were licked a hundred years before we started is no reason for us not to try to win," Atticus said. (ch 9)
Jem is in for a big disappointment. Scout is not convinced that Tom Robinson will be acquitted. She has been watching the same trial as Jem, but with Atticus’s statement in the back of her mind. Jem sees the fairness in the trial system. Atticus defended Tom well, and proved he was not physically able to commit the crime. Therefore, Jem does not understand how Robinson could be convicted.
The conviction is a blow to Jem, but part of becoming an adult. Jem has to accept that there is a lot of unfairness in the world. That unfairness might not be okay, but it cannot be ignored. Atticus stood up for Tom because it was the right thing to do. He is short when he answers Jem because he knows his son is in for a disappointment, and about to lose the naiveté of childhood.
Jem believed that the vedict was going to be not guilty but what he did not realize n actuality Atticus and Tom Robinson never stood a chance, because of his skin color.
Atticus on the other hand seemed to know, as soon as he took up the case that they were never going to win anyway because of the injustice and prejudice in the society. But Atticus never gave up and fought for Tom's justice, but in the end, he fell short