The Gemara says that if someone looks to Shamayim to punish a friend, he gets punished first. The Maharal explains that this person is seeking bad and therefore gets that himself. And although Hashem also punishes, that is for the purpose of the gain for that person or the universe, but it is impossible for a human to seek revenge without the badness.
Any parent can understand this. The difference between the parent punishing and a sibling is a big one.