A Game of Thrones is chock-full of betrayals, treachery, and abandonment. (Also conspiracies, subterfuge, manipulations… should we go on?). Even the people who are incredibly principled do their share of betraying. But remember that betrayals are different than lies (even king of principles, Ned Stark, notes, "We all lie" [23 Arya 2.63]). In order to betray someone, you have to have their trust first. So if there is a lot of betrayal in the world of A Game of Thrones, that means there's also a lot of trust. In a world where no one man can accomplish anything on his own, trust is hugely important; and that means betrayal is a major risk. And a major pain in the neck.