We comment on two embedded case studies of systems effects of successive mid-size projects looking back over 7-10 years, published in Health Policy and Planning. The papers examine humanitarian projects in Sudan and Pakistan and development projects (integrated Community Case Management) in Ethiopia, Malawi, and Mozambique. In this commentary, we summarize the two papers and discuss the overarching substantive and methodological lessons learned.In both development and humanitarian/emergency practice, projects navigate a dynamic space between gap-filling, systems support, and systems strengthening. In this, their contribution to systems strengthening depends heavily on the eco-system of government, development partners, and donors. Systems strengthening presents great challenges in definition, implementation, and measurement. Nonetheless, project implementers can and should renew their commitment to strengthening systems for health. This comes with a fundamental requirement for learning and evaluation.