Increasing attention is being paid towards the potential of social innovation in responding to society’s greatest challenges. While measures have been taken to support the flourishing of these innovations, they have thus far been made on ideal models of development, misaligned with what occurs in reality. This has led to the creation of supporting infrastructures that fail to respond to the real needs of social innovators. The paper seeks to provide a picture of the real social innovation development process through a case-based discussion coming from the results of, SIMPACT, a recently concluded EU research project, where nearly 60 cases of SI across Europe were analysed, with a specific focus on their economic foundation. In the article, we will demonstrate how SI – described by existing frameworks as a rational and structured sequence of prompts, proposals, prototyping, sustaining and scaling – actually takes place in constrained contexts and typically develops as a frugal answer to a social problem. The article will highlight how SIs do not take shape in isolation, and how the ecosystem plays a relevant role in making them flourish. The article will offer substantial empirical evidence that a support system is fundamental in making SI thrive, thus providing relevant insights and guidance for policy making, with particular emphasis on the concept of SI ecosystems.