Nelson Mandela went to jail believing in violence, and 27 years later he and his colleagues had slowly and carefully honed the skills, the incredible skills, that they needed to turn one of the most vicious governments the world has known into a democracy. And they did it in a total devotion to non-violence.
Wherever there is injustice, there is anger, and anger is like gasoline - if you spray it around and somebody lights a matchstick, you have an inferno. But anger inside an engine is powerful: it can drive us forward and can get us through dreadful moments and give us power. I learnt this with my discussions with nuclear policy makers.