My personal theory of social change involves two main factors: a key influencer and an incentivized critical mass within a community. I think most social change is started by a key influencer — maybe a single individual, a motivated group, even large businesses. The key influencer gains momentum through different avenues (now that we’ve talked about them, the four levers of change make sense at this stage), but for social change to actually happen, a critical mass of the relevant community needs to be appropriately incentivized.
I know it seems somewhat cynical to already start talking about incentives. I do believe that people will do things out pure internal motivation — however, at a larger scale, most people have different personal priorities, and behaving in a way that promotes a particular social change may not be at the top of the list for a critical number of people unless there are incentives that move it up their priorities list, or makes it easier for them to go along with the social change. A common example of this is environmental behavior: most people say they want to help save the environment, but choosing energy-efficient light bulbs or recycling properly might not be at the top of their priorities list unless they’re incentivized by convenience, lower costs, or sufficient peer pressure/public shaming. Often, the challenge for the key influencer once they have built up enough momentum is thinking about how to change the system such that the incentives are aligned for the social change.