The motivation for creating a green GDP originates from the inherent limitations of GDP has as an indicator of economic performance and social progress. It only assesses gross output, and does not have a mechanism for identifying the wealth and assets that underlie output. This is problematic because it cannot account for permanent or significant depletion or replenishment of these assets. Ultimately, GDP has no capacity to identify whether the level of income generated in a country is sustainable. Richard Stone, one of the creators the original GDP indicator, suggested that while "the three pillars on which an analysis of society ought to rest are studies of economic, socio-demographic and environmental phenomenon", he had done little work in the area of environmental issues.