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
Ruskin's Seven Lamps of Architecture provided seven guides, or 'lamps', for the troubled craftsman, guides for anyone who works directly on material things. These seven are:
The lamp of sacrifice: The willingness to do something well for its own sake.
The lamp of truth: The truth that 'breaks and rents continually'; Ruskin's embrace of difficulty, resistance, and ambiguity.
The lamp of power: Tempered power, guided standards other than blind will.
The lamp of beauty: Which for Ruskin is found more in the detail, the ornament—hand-sized beauty—than in the large design.
The lamp of life: Life equating with struggle and energy, death with deadly perfection.
The lamp of memory: The guidance provided by the time before machinery ruled.
The lamp of obedience: Obedience to the example set by a master's practice rather than by his particular works; otherwise put, strive to be like Stradivari but do not seek to copy his particular violins.