Let's take a very real, concrete example: commercial migratory beekeeping. Even the largest commercial pollination service is more often than not a small family-run concern. Commercial beekeepers can make a comfortable living but still are just one or two months ahead of their creditors (like most of us). They take pride in the fact that their services help keep a variety of foods on America's dinner table.
Now let's say it's February, the beginning of the migratory beekeeping season and Mr. X is ready to truck his thousands of honeybee colonies into the California almond orchards. He discovers his bees aren't doing all that well. The mite count is high in his hives and they seem to have dysentery. A long-term sustainable approach might be to let Darwinian selection weed out the weak hives and breed from the survivors, however, that would mean losing many hives and possibly going bankrupt. Not only would this threaten his business but also his children's college fund, and next mortgage payment. He, instead, takes the short-term route, using miticides and fungicides on his hives, pumping the colonies with HFCS, trucking them out to the fields and hoping for the best. He knows this solution is not sustainable in that it only creates resistant mites and fungi over the long-term but his family does have to eat. So with all his good intentions he decides in favor of non-sustainability.