"Misanthropy ariseth from a man trusting another without having sufficient knowledge of his character, and, thinking him to be truthful, sincere, and honourable, finds a little afterwards that he is wicked, faithless, and then he meets with another of the same character. When a man experiences this often, and more particularly from those whom he considered his most dear and best friends, at last, having frequently made a slip, he hates the whole world, and thinks that there is nothing sound at all in any of them."

Source: Plato (2012). “The Republic and Other Works”, p.260, Anchor