Sustainability is not a constant. It is recognized that there are different levels of sustainability, depending on the supply of resources that can be secured on a continuous basis in each locality. Consequently, for any specific topic in a local project, the types of activity it is possible to undertake and the outcomes it is possible to achieve will differ from place to place. When compared directly, the results achieved by two such projects in places with different social and economic conditions may appear to be very different, but each should be sustainable in the context of its prevailing development circumstances.
This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities. Agenda 21 recommends setting up demonstration models of different types (e.g. socio-economic, environmental conditions) to study methodology and formulate guidelines.
Successful and sustainable projects require a sensible project design which clearly identifies what will be achieved and how it will be achieved. This may appear self-evident, but some well-intentioned projects are started without a realistic project structure. The absence of a workable design typically leads to confusion over the roles and responsibilities of each partner, avoidable duplication of effort, misuse of limited resources, indeterminate measures of success, and, worst, a higher possibility of "drift" during implementation away from the original objective of the project.