The Republic by Plato Part 6 Page 26

There is reason in supposing that the finest natures, when under alien conditions, receive more injury than the inferior, because the contrast is greater.

Certainly.

And may we not say, Adeimantus, that the most gifted minds, when they are ill-educated, become pre-eminently bad? Do not great crimes and the spirit of pure evil spring out of a fulness of nature ruined by education rather than from any inferiority, whereas weak natures are scarcely capable of any very great good or very great evil?

There I think that you are right.

And our philosopher follows the same analogy — he is like a plant which, having proper nurture, must necessarily grow and mature into all virtue, but, if sown and planted in an alien soil,