When considering, designing for, and evaluating social impact, it's important to take both depth & breadth into account. We aim to 1) significantly improve people's lives, and 2) broadly reach as many people as possible.
For instance, a 1 on 1 intervention may be able to holistically change someone's life on multiple dimensions. How can we sustainably expand this to help the many people in need?
Or vice versa, an awareness raising campaign may reach a large # of people cost-effectively. How can we build on this to ensure that it leads to actual action & desired outcomes?
Sometimes, there's a tradeoff between depth & breadth. But often, there are creative ways to increase breadth & depth together. For example, by reaching a community through its key influencers, you can both spread the message further throughout their network and change norms at the environmental level to support behavior change.
This also points to the necessity for addressing complex problems through a bundle of complementary solutions, rather than a single panacea, to multiply social impact.