Growing up is full of crappy people. As in, while one is in the process of growing up one meets all kinds of different people, and some of them are unkind or even evil.
Taran learns about this in “The Black Cauldron.” In this book, the good die and the evil are left living, people trade sides and make decisions for better or ill, and the honorable path is no longer as clear as it once was. Adventuring has a price.
“‘It is strange,’ he said at last. ‘I had longed to enter the world of men. Now I see if filled with sorrow, with cruelty and treachery, with those who would destroy all around them.’
‘Yet, enter it you must,’ Gwydion answered, ‘for it is a destiny laid on each of us. True, you have seen these things. But there are equal parts of love and joy.'”
It is interesting: as the tale evolves, what marks the heroes from the villains in Prydain is their feelings toward one another. The villains see all people as treacherous, as mirrors for the treachery of their own souls. But the heroes view fallen friends with pity and mercy, and wisdom comes for them in recognizing that “in most of us good and bad are closely woven as the threads on a loom; greater wisdom than mine is needed for the judging.”