I'm happy to say I've now lived long enough to confirm that revenge is a waste. Not that I've acted out on many, but my past tormenters provided me opportunity to come up with delicious plans for revenge. Though those thoughts were a comfort in their own way, I'm embarrassed I indulged in them now. Revenge is a waste.
Why? Because now I've seen the end for the cruel.
One of my chief defences against my opponents has been to get inside their head. If I understood their behavior and what made them tick, I could structure our relationship so that they could no longer harm me. I avoided situations that would lead us in to conflict. For every one of their actions, I had a planned reaction. The strategy has worked very well. An unpleasant side-effect is that I've had to come to understand, even empathize, with people with very different motives than I. The picture is not pretty.
I'd say one common characteristic of brutal or cruel people is that they lack a basic self-awareness. They don't know why they do what they do. Their reactions are reflexive and they will repeat their behavior, bull-headed, even when it harms them. They may gain temporary promotion or success, but eventually that blind spot stops them cold. Not only that, they don't have the self awareness or the tools to recognize what is wrong or get past the obstacle. Life becomes a puzzling affair of blind alleys and false starts.
Now I am sorry I indulged in thoughts of revenge. My chief feeling today is of pity. They are trapped in the cage of their own making, with no way of finding their way out.