One way to explain it is to learn from the past through a striking example, a typical symbol of un-sustainability. "The city of Potosi (in Bolivia) was founded in 1545 following the discovery of silver in the Cerro Rico Mountain. By the end of 18th century Potosi had grown into the largest and wealthiest city in Latin America. The price was the lives of hundreds of thousands of Indian forced labourers and thousands of African slaves, as a result of accidents, mercury poisoning and silicosis pneumonia. Nowadays, Potosi is a decaying place and Bolivia one of the poorest countries in the world ..." (quoted from Giusseppe Munda).
Of course, the then prominent ideologies gave plenty of justification for the Spanish conquistadors to make the decisions that lead to this catastrophic scenario. It’s the same today, when we are still making decisions that are having negative impacts on sustainability. They are based on crude mathematic utilitarian models, one of our current's ideology tools. We even apply the same principles to our individual's decision when we consider the positive and negative impacts those decisions will have on our personal situation. Though, the sustainability concept is really starting to influence the processes shaping both our individual and collective behaviors.
Sustainability is making us very conscious that in a decision problem, the rationale, the goal or the outcome are not that important. What really matters is the evaluative learning process going on, not the final decision that we try to make as good as possible. Mathematically, one could say that the optimum is constructed not discovered. This is neither an inductive nor a deductive process. It is constructive by virtue of the sustainability's framework that is constantly evolving, even timely reshaping the collective intelligence involved in the process.
Now, to use the Potosi example, conquistadors will tell us that the decision outcome (exploiting the mine at all costs) was rational, even the decision process could be labeled as rational. Nevertheless, following H. Simon, "... a distinction must be made between the general notion of rationality as an adaptation of available means to ends, and the various theories based on a rationality which is either substantive or procedural". What is really required, a rational decision outcome or a rational decision process? Using our sustainability lens, Potosi may be an example of irrational process leading to a rational outcome. So, should we aim at a new decision-making approach whereby rational outcome are obtained via a rational decision process? Well, if you listen to D. Ariely, the answer is not that simple: we, human, are "Predictably irrational»!
Let me use a metaphor to show why sustainability is important. Un-sustainability is the concept of "making nobody happy somewhere every time" (there is a lasting effect that shows up somewhere even in the future). The time dimension is intertwined with the location dimension to take the inter-generational perspective into account. A utilitarian approach would have us "making somebody happy somewhere sometime" (a compromise through the netting of positive versus negative impacts), a bit like Maria in "West Side Story". The sustainable vision is about "making everybody happy anywhere sometime" (a time will come for universal well-being to happen locally). This time could be now or tomorrow but the 'everybody' make sure all so-called 'interest groups' are taken care of.
For sure, there is the question of somebody's relevance, or the definition of well-being. Though, looking at the metaphor, it allows for 'well-being' to be situational, hence leaving room for different sociological approaches, even subtle meanings of it. The Tsaatan or the Chipayas will argue their view about a well-being that is radically different from ours. Nevertheless, sustainability's universalism is there to provide us with the lenses required when decisions are to be made that will make them happy or unhappy.
Last but not least, the 'body' should encompass more than simply us, human mortals. Each 'body' that has a lifetime in the universe is to be considered either in a representative or in a direct way. So-called 'interest groups' are there to make sure their best option will be picked. Let me be clear about it, sustainability is there to make the decision process a constructive learning experience through which interest-groups will see their option being picked as the best one 'somewhere, sometime'. At a moment in time, at a certain location, a decision will always be the result of the then-enforced valued criteria but let us make sure it is a sustainably-shaped constructed solution, not a model-driven discovered optimum.
Don't worry - Be Happy !