I don't know if I really know enough about the subject to comment on it, but the idea that personality is inherent and inborn seems rather... disconcerting.

[Armin is so not about anything deciding his fate, not even his own genes. But really, would that mean you'd never be able to change? Always stuck to a certain mould, unable to learn from your experiences and grow beyond that?]

It seems to me that... believing people are inherently anything is just an attempt at simplifying the world for one's own comfort.