When you look at pre-Locke European literature, and also at a lot of pre-Locke scientific literature about the human mind and psyche, the big focus tends to be on inborn character and character flaws, and attempts to overcome them. The model is that a human is born with a prefab character or set of propensities, and a prefab palette of virtues and vices, which will either make the person fail or be triumphantly overcome. We see this all over: Plato’s claim that the majority of human souls are irredeemably dominated by base appetites or passions but a few have the ability to work hard and put Reason in charge; the “science” of physiognomy which strove for centuries to figure out the personality from the inborn structure of a person’s face and head; philosophers from Aristotle and Seneca to Augustine to Aquinas talking about how the best way to become virtuous is to identify your flaws and overcome them through rote repetition. We also see it all over pre-modern fiction, from the Iliad where we watch Achilles wrestle with his great flaw anger, to noble Lancelot marred by his weakness to love, to the Inferno where Dante’s journey helps him overcome his tendency toward sins of the she-wolf, to Shakespeare.
John Locke, then, was one linchpin moment in a big change in how we think about psychology (aided by others like Descartes on one end and Rousseau and Freud on the other). This transformation led to a rejection of old ideas of inborn character and character flaws, and replaced them with Locke’s famous tabula rasa idea, that people are born inherently blank, and growing up is a process of forming and creating one’s character based on experiences rather than watching a prefabricated inborn personality working forward to its conclusion. This new idea became extremely widespread in Europe with amazing speed (thanks to the printing press and the Enlightenment) and resulted in a remarkably quick change in how people thought people thought.
This was in turn reflected in fiction, and created a new sense of how character progression should work. The post-Locke audience (whether reading Austen, Dickens, Asimov or Marvel Comics) expects to watch a character develop and acquire a personality over time, gaining new attributes, growing and transforming with new experiences. If the character has deep flaws, we expect them to be the result of experiences, traumas, betrayals, disasters, a spoiled childhood, something. We generally aren’t satisfied if the villain is evil because she or he was born that way, and we love it when an author successfully sets up a beloved character’s great moment of failure or weakness by showing us the earlier experience which led to it. This is an oversimplification, of course, but the gist of it gets at the issues as they relate to Shakespeare’s reception today.