Why was Jem so certain that tom would be acquitted?

Jem was certain that Tom Robinson would be acquitted because he believed in the fundamental fairness of the justice system and the evidence presented in the trial, which he thought clearly demonstrated Tom's innocence. He had faith in the integrity of the jurors and was influenced by the moral teachings of his father, Atticus Finch, who defended Tom. Jem's optimism also stemmed from his youthful idealism, which made him believe that truth and justice would prevail in the face of prejudice.