"The cruel man troubles his own flesh"
As it was, it made less of an impression than it otherwise would have only because of the far greater cruelty, and much more consistently, of the American occupiers. They, too, were defeated by their own cruelty.
Then, too, every one of Israel's massacres in Gaza moves that state toward history's compost heap, as does its calculated and scientific cruelty in the West Bank. Its massacres and systematic torture during its occupation of South Lebanon created Hizbollah from the formerly friendly Lebanese Shi'a population.
These principles work in the smallest conflicts in the same way - in our families, our workplaces, and schools. Your own cruelty will defeat you in the end. I know that you can bully and terrorize people by means of cruelty, which is why it is so popular, but it never ends well.
The other half of the proverb also holds true, "the merciful man does good to his own life." Let's try it, not to be nice, but to do good to our own flesh.