I don't deny at all that the hound feels a lifetime worth of resentment and hatred towards the mountain. The point is the mountain doesn't, this fight is entirely one sided, and his cruelness towards his little brother is no different than his cruelness towards every other person.

IMO the take away from their interactions is that you can be influenced and hyperfixated on one person, and your obsession and hate means nothing. The other person is out here living life and you in a dark room cursing their name and missing out on living.