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
Tange put Tsukiji as the centre of his plan, which now seems grandiose and delusional. His design for the Dentsu building had much in common with the Metabolist philosophy of the 1960s, which maintained that buildings needed to continually evolve in a flexible way.
...With [the Nakagin Capture Tower], Kurokawa's Metabolist philosophy was fully realized. After it was completed, however, it became almost impossible to switch over the capsules - indeed, since its completion, not one of the capsules has been moved. As a result, the Metabolist movement has been forgotten. Yet its core principles, which sought to draw architectural lessons from living organisms, has much inspiration to offer society today.