This famous stunt in the movie was actually built around what went wrong with the original stunt. Keaton intended to leap from one building onto the roof of another building, but he fell short, smashing into the brick wall and falling into a net off-screen. He was injured badly enough to be laid up for three days. But when he saw the film (his camera operators were instructed to always keep filming, no matter what happened), he not only kept the mishap, he built on it, adding the fall through three awnings, the loose downspout that propels him into the firehouse, and the slide down the fire pole. (The Three Ages - 1923)

This is just amazing.

(Source: maudit, via dinnerwithnormanbates)