We discover too late that we have turned a blind eye to the extinction of a species that is essential to the balance of life in a particular context. Or we discover too late that the importation of a foreign life-form, animal or vegetable, has upset local ecosystems, damaging soil or neighbouring life-forms. We discover that we have come near the end of supplies-of fossil-fuels for example -on which we have built immense structures of routine expectation.
