Sustainability means the ability to last, the ability to keep going. It means development for the long-term. In personal terms, that means a commitment to our children and our grandchildren. A commitment to the continuation of society and its evolution, its enrichment not just for a little while, but for as long as we can see into the future. Rather, it's about leaving the Earth and the society better off as a result of our having been here.
Sustainability is an intrinsic human value.
It is an approach to immortality. People wouldn't have children if they didn't care about sustainability. Sustainability is a well-understood idea in the realm of economics, where every bank, every company, knows the difference between living from your income and drawing down your capital. Drawing down your capital may allow you to live very well for a short time, but it is not sustainable in economic terms. Sustainability means preserving, and preferably enhancing, the capital assets from which you live.