It's relatively common that the reason that Alice wants to kill Bob is because Bob killed Charlie. Revenge seems pretty straightforward. But it gets a lot more murky when Charlie was trying to kill Bob and Bob was just defending himself. They were in a war, it was a fight, Charlie surprised Bob at the worst time, it was an accident, the list goes on. He didn't really want to kill Charlie, and would have avoided doing so if possible. It's likely he regrets it greatly. That doesn't matter to Alice, though. Even if unknown to her Charlie was an assassin that had killed hundreds of people and Bob is just some bodyguard that happened to take him down, Bob has to pay.