To build a folly is essentially to do something a second time, something at an inopportune moment. That something is always the memory of something forgotten, about which we can paradoxically say "There it is again."
Follies were misunderstood, purposeless constructions. They were often only small, extravagant gestures in a garden, easily whisking off the imagination to distant lands, a sort of time capsule built to awaken the memory and induce surprise in passers-by. They marked locations, organized secondary paths in a park, or simply predicted the arrival of better times—a demarcation, a sacred spot, a mysterious trail, a hill whose tragic rocky nature begged for a tower, a party, or the arrival of summer.
“It is demonstrably true that things cannot be other than as they are. For, everything having been made for a purpose, everything is necessarily for the best purpose.” — Professor Pangloss
“Controlled environments” are another of modernism’s great obsessions. Extravagant amounts of energy are spent to keep buildings—as well as skyway systems, shopping malls, and domed stadia—at a constant temperature year-round via entirely mechanical means. The folly is not simply a touchy-feely isolation from the authenticities of nature, which can admittedly be cruel, but a larger disciplinary presumption that seeks to extend the centralized authority (central air, central government) of power ever more comprehensively. It is possible that this particular hubris may have pushed Gaia to the tipping point.