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Those afflicted with BPD suffer from emotional instability—in Katherine’s case, almost always caused by feelings of rejection or abandonment. They suffer from cognitive distortions, where they see the world in black and white, with anyone who isn’t actively ‘with them’ being considered an enemy. They are also prone to catastrophising, where they make logical leaps from minor impediments in their plans to assumptions of absolute ruin. BPD is often characterised by extremely intense but unstable relationships, as the sufferer gives everything that they can to a relationship in their attempts to ensure their partner never leaves but instead end up burning themselves out and blaming that same partner for the emotional toll that it takes on them. The final trait of BPD is impulsive behaviour, often characterised as self-destructive behaviour. In Katherine’s case, this almost always manifested itself in her hair-trigger temper. When she was enraged, it was like she lost all rational control over her actions, seeing everyone else as her enemies. This manifested itself in the ridiculous bullying she conducted at school, in her lashing out when she failed her test and in the vengeance that she took on her sexual abusers. It is likely that she inherited this disorder from her mother, who showed many of the same symptoms, and that they were exacerbated by her chaotic home life and the lack of healthy relationships in the adults around her that she might have modelled herself after. With Katherine, it was like a Jekyll and Hyde switch took place when her temper was raised. The charming, eager-to-please girl who usually occupied her body was replaced with a furious, foul-mouthed hellion bent on exacting her revenge no matter what the cost. In itself, this could have been an excellent excuse for almost everything that she did wrong in her life, up to and including the crimes that she would later be accused of. Unfortunately, this sort of ‘flipped switch’ argument doesn’t hold up when you consider that her choice to arm herself with a lethal weapon was premeditated. Part of this may certainly have been the cognitive distortion that Katherine experienced, telling her that everyone else was out to get her and that she had to defend herself, but ultimately, she was choosing to give a weapon to a person who would use it to end lives, if she had the opportunity. Assuming that this division of personalities actually existed, then ‘good’ Katherine was an accomplice to ‘bad’ Katherine, giving her the material support and planning that she needed to commit her vicious attacks.
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Ryan Green (Man-Eater: The Terrifying True Story of Cannibal Killer Katherine Knight)