Gandhi's Satyagraha & Social Change, with Sujata Gadkar-Wilcox

Satyagraha, one of Gandhi's most influential teachings, stresses "passive resistance" in the face of injustice. Qunnipiac's Gadkar-Wilcox saw a powerful example of this in regards to a debate in India over sanitary napkins and she also sees it as Florida high school students push legislators for stricter gun control. Why is this tactic or "disposition" so effective?