This is a very broad, open question that isn't likely to be very quantifiable. As such, folks can only offer anecdotes and opinions. Perhaps if you had a much more specific question about what you actually need to know, the folks here might be more able to help you. These type of talking-points and discussion questions are better asked in a discussion forum or chat room. It will surely be an interesting discussion, it's just not well-suited to this site
I would like to argue that this is quantifiable, although not necessarily on-topic at Politics SE (probably moreso at History SE). In fact, an entire book has been published addressing this question:
Erica Chenatoweth and Maria Stephan, Why Civil Resistance Works, Colombia University Press, 2011.
I'm sure many of the results are open for interpretation and debatable, but the precise point that it's not quantifiable, I disagree with. One can count historical non-violent movements, make an estimate of the number of participants, and an observation as to whether or not the effects have been achieved or not.