This is a quote from Isaac Botkin’s article titled “Screenwriting: Three-Act Structure”.
“The first act is exposition, not much conflict. Then in Act II the fight begins, and our hero is up and down, taking the audience on a roller coaster ride of success and defeats, until the third act, where he recovers from some crushing blow and rises to victory…
“Act II encapsulates the jeopardies and tensions that fill out the drama and contains almost the entire story of the film. Here the hero is in for a rude shock as he is run up against the machinations of the villain(s). His tests are often moral as well as circumstantial. If he’s human, he stumbles or fails several times. This is so that he can succeed only by persevering and making the right, difficult moral choices. This is what makes him a hero. Let me repeat that because it’s such an important definition. The hero is heroic because he chooses morality over compromise. This is real heroism.”