An ingénue is a dramatic and literary archetype. “The ingénue symbolizes the mutable character par excellence, the blank slate in search of an identity,” the French scholar Julia V. Douthwaite wrote about the role of the ingénue in Ancien Régime French fiction. The ingénue is defined by her age — that crepuscular moment between adolescence and adulthood — and also by her innocence. A naïf in a complex, urbane, foreign world, she moves unaware of the hypocrisy, duplicity and exploitation all around her. She is credulous and vulnerable and dependent on a protective paternal figure and lives in constant peril of being exploited or corrupted by some lurking cad or villain. This threat is the central tension of her life. What makes her interesting are the questions of how she will navigate this world, who she will become and what will become of her. Traditionally, there have existed two possible outcomes: marriage (whether successful or ruinous) or death.
From New York Times, Carina Chochano, April 22, 2011
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So, at the very heart of it, the ingénue doesn't know she is about to be tricked into having sex.
Once she realizes that the men in her life are willing to use her, she becomes a different person. Either she takes control of her life and becomes "worldly" or "cool"; or she becomes a victim, destined to appear on Oprah.