Members of a society are connected through a web of social relationships shaped by family and friendship, involving care, support and mutual obligations, as well as through shared norms, rights and collective arrangements that structure responsibilities across generations. They are also linked through economic exchanges through markets and public institutions. These connections vary over the life course, as individuals move between roles as recipients and providers of support. Children rely heavily on resources provided by families and public investments in education, health care and other services. During their working years, adults con-tribute more than they receive, supporting children and older generations both directly within families and indirectly through taxes and other transfers that finance public programs. Older persons rely on the mutual sup-port of families and the public sector, supplemented by their own savings. They may also continue working―often in the informal sector―motivated by economic necessity or a desire for continued engagement.
These intergenerational exchanges of resources―whether through monetary flows, time transfers or implicit social contracts―constitute the hidden generational economy, a network of reciprocity that sustains prosperity over the life course. Viewed in this context, the central unifying principle of the SDGs―“Leaving no one behind”―is not an act of charity toward people experiencing vulnerability. Rather, it is a recognition that we all take turns receiving and giving over our lives, and that the system works best when everyone is included.