It is a commonly misattributed quote, often associated with the book and its main character, Atticus Finch. The closest the book comes to expressing this idea is through Atticus's own words about courage:
* "Courage is not a man with a gun in his hand. It's knowing you're licked before you begin but you see it through no matter what." This line is spoken by Atticus in Chapter 11, when he explains to Scout why he defends Tom Robinson, even though he knows he's likely to lose the case.
However, the exact wording of the popular quote, with the word "real" before "courage," doesn't appear in the book. This variation likely developed over time, as people remembered and shared the sentiment of Atticus's words.