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
If we reach such a very ordinary state of daily life, and then back it up with building and construction that comes from the depths in us, then that gradually accumulates our value in the world, all of us together as a whole. Later, then, perhaps hundreds of years later, people will look back at our stones and say to themselves, "My word, those people way back then — they certainly knew how to live," and they would say this because they could see the lingering whispers in the walls and mosses, and could read them, and could treasure them, and would learn from these traces how to live like that again.