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
There is a Japanese catchphrase, community suru, literally "making" or "doing" community. I will never forget the queasy feeling that came over me when I first heard that term, phrased as if community were a kind of event.
Hold an event, bring people together, get people who might otherwise never meet to interact. It's a wonderful thought. I have nothing against events per se. However, if they are not spontaneous and voluntary, they will not last. That is my objection to the keep-it-lively concept of community. The perception of community as event stems, I think, from a yearning for the festivals and rituals that once flourished in rural communities in Japan. But those events occurred precisely because a community existed, not the other way around.