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
You might think that Mario 64 was built with tickets and sprints, but, according to interviews, there was no master plan, only the principles that the game should feel good and be fun. They started with just Mario in a small room, and tuned his animations and physics until he felt nice and responsive. After that, the levels were also created as they went, with the designers, developers, and director going back and forth using sketches and prototypes.
Building like this is never a straight line. Ideas and code get left on the cutting room floor because part of innovation is questioning whether what you made should exist. The process is cyclical and iterative, looking something like this.