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
I cannot perceive for you. I can conceive for you and we can then in a sense hold a general agreement about quality of conception and we may all operate under it and that's what is known as a common agreement. But the area of perceiving as such is totally individual, there's no way that we carry it in that sense.
This is not an antisocial gesture; it is in fact a highly ethical one, since trying to get another person to see what and how you see has the potential to become a violation of the other's own autonomy:
There is nothing more unethical than having ambitions for someone else's mind.