Violence is rarely the answer, but when it is … it is the only answer. [emphasis added]Watch the full talk here*. It's 17 minutes, and well worth the time. Pay attention to the no-context "self-defense" situation presented, and note when he says that when asked, most non-criminals will place themselves in the role perceived as a "victim", while criminals will place themselves in the role that looks like it will prevail.
This is just one more data point supporting the idea that the hardest parts about effective self-defense are developing the mindset and overcoming the deeply-ingrained aversion to violence. Seeing violence as a tool — one that could be equally used for good or evil — is a vital part of that development.
* - Also, if you're a fan of TED Talks, you know that audience interaction often comes into play, but due to reported technical difficulties on this production (i.e. the audience-facing microphones failing) you hear almost no audience reactions. Rest assured, they are reacting, and it's still a good video.