In international development there is a tension between the drive to "scale what works" and the fundamental reality that the world is complex, and solutions discovered in one place often can't be easily transported to different contexts.
At Innovations for Poverty Action, we use randomized controlled trials to measure which solutions to poverty work and why. We believe that this methodology can help to alleviate poverty, and yet we don't advocate focusing solely on programs that are "proven" to work in this way. One risk of funding only "proven" and therefore "provable" interventions – the "moneyball of philanthropy" – is that interventions proven to work in one place could be transposed to new situations without attention to context, which could be a disaster. Also, interventions that cannot easily be subjected to rigorous evaluation may not get funding.
The risk of the other extreme – focusing only on the details of a complex local environment – is that we may fail to uncover important lessons or innovative ideas that can improve the lives of millions in other places. Focusing only on the complexity and uniqueness of each situation means never being able to use prior knowledge, dooming one to constantly reinvent the wheel.