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
We are not now inclined to regard modern heating and cooling systems as representative of a spiritual realm. The physical principles involved in their operation are thoroughly understood; there is no mystery about them. They are simply functional, designed according to straightforward engineering practice to serve their intended function as efficiently and conveniently as possible.
And yet functionalism itself can be a kind of religion.
...From the fifties and sixties we have inherited numerous heating and cooling systems created within an ethos of universal convenience. Machines to maintain our thermal comfort were conceived of as mechanical servants, providing for our every need while, like an English butler, remaining as unobtrusive as possible.