The maturation of a story’s protagonist—as “growth” eventuated through the progression of the narrative—provides a source of dynamism that can keep a film from being static, or falling flat for lack of character development. At the same time, a good screenwriter is careful not to overdo it, lest a character’s internal transition occur too quickly in terms of the story to be believable. In Dallas Buyers Club, Ron Woodroof—played by Matthew McConaughey—“turns on a dime” in his attitude toward gays. The flip is hardly believable. The question is why.
From: "Dallas Buyers Club"