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
"Artists need to be in there from the start, making the argument for quality. The key to this thing is, for example, if you give an engineer a set of criteria which does not include a quality quotient, as it were—that is, if this sense of the quality, the character of the place, is not a part of his original motivation—he will then basically put the road straight down the middle. He has no reason to curve it. But if I can convince him that quality is absolutely a worthwhile thing and we can work out a way in which the road can be efficient and also wander down by the river, then we essentially have both: he provides his sort of expertise in that the road works, I provide quality in that it passes by the river. In that way, art gets built into the criteria from the beginning rather than being added on afterward."