Will evil prevail?

I've just finished watching a compelling lecture from Samantha Power, academic and foreign policy adviser to Obama, in answer to the question: Will evil prevail? Power has spent many years researching and writing on genocide and I'm familiar with her writing on the Rwandan Genocide, in particular.
This lecture was a challenging reminder on each individual persons role in shaping history and the possibility for change. Power shares the story of a UN envoy, Sergio Vieira de Mello, in illustrating creative ways, and sometimes misunderstood ways, of affecting change.
Most moving is her final statement.... "Will evil prevail?.... Not unless we let it."
http://www.youtube.com/watch?v=_lZ55gHabAA