Atticus says, "Simply because we were licked a hundred years before we started is no reason for us not to try to win." What does he mean?
Atticus is referring to slavery and prejudice in general. For the last hundred years at the time of the novel, African-Americans had been considered less than human. The majority of people in the story are prejudiced against them. Atticus is fighting a battle to clear a black man's name in spite of a white woman's testimony, and recognizes this as a losing battle. However, because he believes that all men are created equal, he wants to try to win for the sake of Tom Robinson, for the sake of equality, for the sake of all people's rights in this world. Society has already "licked" (or "beaten") Atticus and his defendant in the sense that most people are already convinced that Tom is in the wrong simply because of the color of his skin, but Atticus continues to fight for the rights of a black man because his personal code of ethics demands nothing less than this.